diff --git a/.gitignore b/.gitignore
index cda1d4da..677f1625 100644
--- a/.gitignore
+++ b/.gitignore
@@ -78,3 +78,6 @@ Resources/InfoPlist/Info.plist
 
 ### Using tests
 Tests/**/*.plist
+
+### Changelog
+Changelog/next.md
diff --git a/Changelog/1.7.0.md b/Changelog/1.7.0.md
new file mode 100644
index 00000000..6962b9f3
--- /dev/null
+++ b/Changelog/1.7.0.md
@@ -0,0 +1,8 @@
+## New features
+- Added to change theme feature.
+
+## Enhancements
+- Prevent adding duplecate word.
+
+## Fixed
+- Fixed memory leak for view controller.
diff --git a/Changelog/next.md b/Changelog/next.md
deleted file mode 100644
index e666edce..00000000
--- a/Changelog/next.md
+++ /dev/null
@@ -1,3 +0,0 @@
-## Enhancements
-
-## Fixed
diff --git a/Project.swift b/Project.swift
index f51d686f..28c76ca5 100644
--- a/Project.swift
+++ b/Project.swift
@@ -23,7 +23,6 @@ func targets() -> [Target] {
                 .external(name: ExternalDependencyName.rxUtilityDynamic),
                 .external(name: ExternalDependencyName.swinject),
                 .external(name: ExternalDependencyName.swinjectExtension),
-                .external(name: ExternalDependencyName.then),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -42,11 +41,6 @@ func targets() -> [Target] {
             ],
             appendSchemeTo: &disposedSchemes
         )
-        + Target.module(
-            name: "FoundationExtension",
-            hasTests: true,
-            appendSchemeTo: &schemes
-        )
         + Target.module(
             name: "Utility",
             scripts: [
@@ -72,7 +66,6 @@ func targets() -> [Target] {
                 .package(product: ExternalDependencyName.googleSignIn),
                 .external(name: ExternalDependencyName.rxSwift),
                 .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.extendedUserDefaults),
                 .external(name: ExternalDependencyName.extendedUserDefaultsRxExtension),
                 .external(name: ExternalDependencyName.swinject),
                 .external(name: ExternalDependencyName.swinjectExtension),
@@ -91,37 +84,32 @@ func targets() -> [Target] {
             appendSchemeTo: &disposedSchemes
         )
         + Target.module(
-            name: "iOSSupport",
+            name: "IOSSupport",
             resourceOptions: [.own],
             dependencies: [
                 .target(name: "Domain"),
                 .target(name: "Utility"),
+                .external(name: ExternalDependencyName.foundationPlus),
                 .external(name: ExternalDependencyName.rxSwift),
                 .external(name: ExternalDependencyName.rxCocoa),
                 .external(name: ExternalDependencyName.rxUtilityDynamic),
                 .external(name: ExternalDependencyName.reactorKit),
                 .external(name: ExternalDependencyName.snapKit),
                 .external(name: ExternalDependencyName.then),
+                .external(name: ExternalDependencyName.toast),
+                .external(name: ExternalDependencyName.sfSafeSymbols),
+                .external(name: ExternalDependencyName.swinject),
+                .external(name: ExternalDependencyName.swinjectExtension),
+                .package(product: ExternalDependencyName.swiftCollections),
             ],
-            appendSchemeTo: &disposedSchemes
+            appendSchemeTo: &schemes
         )
         + Target.module(
             name: "WordChecking",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.sfSafeSymbols),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -135,7 +123,7 @@ func targets() -> [Target] {
             name: "WordCheckingExample",
             product: .app,
             infoPlist: .file(path: "Resources/InfoPlist/InfoExample.plist"),
-            sourcesPrefix: "iOSScenes",
+            sourcesPrefix: "IOSScenes",
             dependencies: [
                 .target(name: "WordChecking"),
                 .target(name: "DomainTesting"),
@@ -144,22 +132,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "WordList",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .target(name: "WordDetail"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.sfSafeSymbols),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -171,20 +147,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "WordDetail",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -196,21 +162,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "WordAddition",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .target(name: "FoundationExtension"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -222,20 +177,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "UserSettings",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -250,7 +195,7 @@ func targets() -> [Target] {
             name: "UserSettingsExample",
             product: .app,
             infoPlist: .file(path: "Resources/InfoPlist/InfoExample.plist"),
-            sourcesPrefix: "iOSScenes",
+            sourcesPrefix: "IOSScenes",
             dependencies: [
                 .target(name: "UserSettings"),
                 .target(name: "DomainTesting"),
@@ -259,22 +204,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "LanguageSetting",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "Domain"),
-                .target(name: "iOSSupport"),
-                .target(name: "FoundationExtension"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.snapKit),
-                .external(name: ExternalDependencyName.then),
-                .external(name: ExternalDependencyName.toast),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
-                .package(product: ExternalDependencyName.swiftCollections),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -284,18 +217,26 @@ func targets() -> [Target] {
             ],
             appendSchemeTo: &schemes
         )
+        + Target.module(
+            name: "ThemeSetting",
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
+            dependencies: [
+                .target(name: "IOSSupport"),
+            ],
+            hasTests: true,
+            additionalTestDependencies: [
+                .target(name: "DomainTesting"),
+                .external(name: ExternalDependencyName.rxBlocking),
+            ],
+            appendSchemeTo: &schemes
+        )
         + Target.module(
             name: "PushNotificationSettings",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "iOSSupport"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -308,7 +249,7 @@ func targets() -> [Target] {
             name: "PushNotificationSettingsExample",
             product: .app,
             infoPlist: .file(path: "Resources/InfoPlist/InfoExample.plist"),
-            sourcesPrefix: "iOSScenes",
+            sourcesPrefix: "IOSScenes",
             dependencies: [
                 .target(name: "PushNotificationSettings"),
                 .target(name: "DomainTesting"),
@@ -317,16 +258,10 @@ func targets() -> [Target] {
         )
         + Target.module(
             name: "GeneralSettings",
-            sourcesPrefix: "iOSScenes",
-            resourceOptions: [.additional("Resources/iOSSupport/**")],
+            sourcesPrefix: "IOSScenes",
+            resourceOptions: [.additional("Resources/IOSSupport/**")],
             dependencies: [
-                .target(name: "iOSSupport"),
-                .external(name: ExternalDependencyName.rxSwift),
-                .external(name: ExternalDependencyName.rxCocoa),
-                .external(name: ExternalDependencyName.rxUtilityDynamic),
-                .external(name: ExternalDependencyName.reactorKit),
-                .external(name: ExternalDependencyName.swinject),
-                .external(name: ExternalDependencyName.swinjectExtension),
+                .target(name: "IOSSupport"),
             ],
             hasTests: true,
             additionalTestDependencies: [
@@ -336,9 +271,9 @@ func targets() -> [Target] {
             appendSchemeTo: &schemes
         )
         + Target.module(
-            name: "iPhoneDriver",
+            name: "IPhoneDriver",
             dependencies: [
-                .target(name: "iOSSupport"),
+                .target(name: "IOSSupport"),
                 .target(name: "WordChecking"),
                 .target(name: "WordList"),
                 .target(name: "WordAddition"),
@@ -348,11 +283,8 @@ func targets() -> [Target] {
                 .target(name: "PushNotificationSettings"),
                 .target(name: "GeneralSettings"),
                 .target(name: "Infrastructure"),
-                .external(name: ExternalDependencyName.swinject),
+                .target(name: "ThemeSetting"),
                 .external(name: ExternalDependencyName.swinjectDIContainer),
-                .external(name: ExternalDependencyName.sfSafeSymbols),
-                .external(name: ExternalDependencyName.then),
-
             ],
             appendSchemeTo: &disposedSchemes
         )
@@ -366,7 +298,7 @@ func targets() -> [Target] {
                 .additional("Resources/InfoPlist/Product/**"),
             ],
             dependencies: [
-                .target(name: "iPhoneDriver"),
+                .target(name: "IPhoneDriver"),
             ],
             settings: .settings(),
             appendSchemeTo: &schemes
@@ -381,7 +313,7 @@ func targets() -> [Target] {
                 .additional("Resources/InfoPlist/Dev/**"),
             ],
             dependencies: [
-                .target(name: "iPhoneDriver"),
+                .target(name: "IPhoneDriver"),
             ],
             settings: .settings(),
             appendSchemeTo: &schemes
@@ -406,7 +338,7 @@ func targets() -> [Target] {
                 sources: "Tests/\(PROJECT_NAME)UITests/**",
                 dependencies: [
                     .target(name: "\(PROJECT_NAME)Dev"),
-                    .target(name: "iOSSupport"),
+                    .target(name: "IOSSupport"),
                     .target(name: "Utility"),
                     .package(product: "Realm"),
                 ]
diff --git a/QA.md b/QA.md
index 4e0de536..fe8a9b67 100644
--- a/QA.md
+++ b/QA.md
@@ -1,10 +1,10 @@
 #Version
-1.5.0
+1.7.0
 
 ##Common
 - Localization 적용 확인
 
-##WordCheking
+## WordCheking
 
 - 단어 추가 시 리스트에 반영
 - 단어 암기 완료 시 리스트에 반영
@@ -12,20 +12,31 @@
 - 단어 앞, 뒤 이동 정상 작동
 - 마지막 단어 암기 완료 표시 시 '단어 없음' 문구 출력
 - 마지막 단어 삭제 시 '단어 없음' 문구 출력 
+- 중복 단어 추가 시 중복 단어 Toast 메세지 표시 확인
 
-##WordList
+## WordList
 
 - 현재 단어 수정 시 암기 화면에 반영
 - 현재 단어 삭제 시 암기 화면에 반영
 - 현재 단어 암기 완료 표시 시 암기 화면에 반영
 - 현재 단어 없을 때 단어 암기중 표시 시 화면에 반영
 
-##WordSearch
+## WordAddition
+
+- 단어 추가 시 중복 단어일 때 중복 경고 메세지 표시 확인
+- 단어 추가 시 입력된 단어가 없을 때 완료 버튼 비활성화 확인
+
+## WordDetail
+
+- 단어 편집 시 중복 단어일 때 중복 경고 메세지 표시 확인
+- 수정 사항이 존재할 때 취소 확인 ActionSheet 표시 확인
+
+## WordSearch
 
 - 단어 검색 이상 여부 확인
 - 단어 검색 후 수정 시 리스트&암기 화면에 바로 적용 여부 확인
 
-##Settings
+## Settings
 
 - Source language / Translation language 변경시 번역 사이트에 정상 적용 확인
 - 구글 드라이브 로그인 여부에 따라 로그아웃 버튼 표시
diff --git a/Resources/iOSSupport/Localization/en.lproj/Localizable.strings b/Resources/iOSSupport/Localization/en.lproj/Localizable.strings
index 301a3fc5..a4273419 100644
--- a/Resources/iOSSupport/Localization/en.lproj/Localizable.strings
+++ b/Resources/iOSSupport/Localization/en.lproj/Localizable.strings
@@ -38,6 +38,9 @@ all = "All";
 there_are_no_words = "There are no words.";
 quick_add_word = "Quick add word";
 "%@_added_successfully" = "[ %@ ] added successfully";
+already_added_word = "Already added word.";
+"%@_added_failed" = "[ %@ ] added failed.";
+
 settings = "Settings";
 translation_language = "Translation language";
 
@@ -66,9 +69,16 @@ dailyReminderFooter = "Sends a daily push notification at the time you set.";
 general = "General";
 haptics = "Haptics";
 hapticsSettingsFooterTextWhenHapticsIsOn = "Enable haptics for interactions.";
-hapticsSettingsFooterTextWhenHapticsIsOff = "Disable haptics for interactions";
+hapticsSettingsFooterTextWhenHapticsIsOff = "Disable haptics for interactions.";
+
+theme = "Theme";
+system_mode = "System mode";
+light_mode = "Light mode";
+dark_mode = "Dark mode";
 
 more_menu = "More menu";
 memorize_words = "Memorize words";
 next_word = "Next word";
 previous_word = "Previous word";
+
+duplicate_word = "Duplicate word.";
diff --git a/Resources/iOSSupport/Localization/ko.lproj/Localizable.strings b/Resources/iOSSupport/Localization/ko.lproj/Localizable.strings
index 59a2ee5a..b5966b46 100644
--- a/Resources/iOSSupport/Localization/ko.lproj/Localizable.strings
+++ b/Resources/iOSSupport/Localization/ko.lproj/Localizable.strings
@@ -38,6 +38,8 @@ all = "전체";
 there_are_no_words = "단어가 없습니다.";
 quick_add_word = "빠른 단어 추가";
 "%@_added_successfully" = "[ %@ ] 추가 성공";
+already_added_word = "이미 추가된 단어입니다.";
+"%@_added_failed" = "[ %@ ] 단어 추가 실패";
 
 settings = "설정";
 languages = "언어";
@@ -68,7 +70,14 @@ haptics = "진동";
 hapticsSettingsFooterTextWhenHapticsIsOn = "상호 작용에 대한 진동을 사용합니다.";
 hapticsSettingsFooterTextWhenHapticsIsOff = "상호 작용에 대한 진동을 사용하지 않습니다.";
 
+theme = "테마";
+system_mode = "시스템 설정 모드";
+light_mode = "라이트 모드";
+dark_mode = "다크 모드";
+
 more_menu = "메뉴 더보기";
 memorize_words = "단어 암기";
 next_word = "다음 단어";
 previous_word = "이전 단어";
+
+duplicate_word = "중복 단어입니다.";
diff --git a/Sources/Domain/Interfaces/Services/LocalNotificationService.swift b/Sources/Domain/Interfaces/Services/LocalNotificationService.swift
index 35284aed..d2a03c10 100644
--- a/Sources/Domain/Interfaces/Services/LocalNotificationService.swift
+++ b/Sources/Domain/Interfaces/Services/LocalNotificationService.swift
@@ -29,6 +29,6 @@ public protocol LocalNotificationService {
 
     /// 매일 알림을 설정한 마지막 시각을 반환합니다.
     ///
-    /// /// - throws: 저장된 시각이 없을 때 Error 를 던집니다.
+    /// - throws: 저장된 시각이 없을 때 Error 를 던집니다.
     func getLatestDailyReminderTime() throws -> DateComponents
 }
diff --git a/Sources/Domain/Interfaces/UseCases/ExternalStore/ExternalStoreUseCaseError.swift b/Sources/Domain/Interfaces/UseCases/ExternalStore/ExternalStoreUseCaseError.swift
new file mode 100644
index 00000000..e5a6b8b0
--- /dev/null
+++ b/Sources/Domain/Interfaces/UseCases/ExternalStore/ExternalStoreUseCaseError.swift
@@ -0,0 +1,17 @@
+//
+//  ExternalStoreUseCaseError.swift
+//  Domain
+//
+//  Created by Jaewon Yun on 2/12/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import Foundation
+
+public enum ExternalStoreUseCaseError: Error {
+
+    case noCurrentUser
+
+    case noPresentingConfiguration
+
+}
diff --git a/Sources/Domain/Interfaces/UseCases/ExternalStoreUseCaseProtocol.swift b/Sources/Domain/Interfaces/UseCases/ExternalStore/ExternalStoreUseCaseProtocol.swift
similarity index 100%
rename from Sources/Domain/Interfaces/UseCases/ExternalStoreUseCaseProtocol.swift
rename to Sources/Domain/Interfaces/UseCases/ExternalStore/ExternalStoreUseCaseProtocol.swift
diff --git a/Sources/Domain/Interfaces/UseCases/Notification/NotificationsUseCaseError.swift b/Sources/Domain/Interfaces/UseCases/Notification/NotificationsUseCaseError.swift
new file mode 100644
index 00000000..1a104b23
--- /dev/null
+++ b/Sources/Domain/Interfaces/UseCases/Notification/NotificationsUseCaseError.swift
@@ -0,0 +1,13 @@
+//
+//  NotificationsUseCaseError.swift
+//  Domain
+//
+//  Created by Jaewon Yun on 2/12/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import Foundation
+
+public enum NotificationsUseCaseError: Error {
+    case noWordsToMemorize
+}
diff --git a/Sources/Domain/Interfaces/UseCases/NotificationsUseCaseProtocol.swift b/Sources/Domain/Interfaces/UseCases/Notification/NotificationsUseCaseProtocol.swift
similarity index 100%
rename from Sources/Domain/Interfaces/UseCases/NotificationsUseCaseProtocol.swift
rename to Sources/Domain/Interfaces/UseCases/Notification/NotificationsUseCaseProtocol.swift
diff --git a/Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseError.swift b/Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseError.swift
new file mode 100644
index 00000000..b51ebcba
--- /dev/null
+++ b/Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseError.swift
@@ -0,0 +1,14 @@
+//
+//  UserSettingsUseCaseError.swift
+//  Domain
+//
+//  Created by Jaewon Yun on 2/12/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import Foundation
+
+public enum UserSettingsUseCaseError: Error {
+    case noPendingDailyReminder
+    case noNotificationAuthorization
+}
diff --git a/Sources/Domain/Interfaces/UseCases/UserSettingsUseCaseProtocol.swift b/Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseProtocol.swift
similarity index 90%
rename from Sources/Domain/Interfaces/UseCases/UserSettingsUseCaseProtocol.swift
rename to Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseProtocol.swift
index 1051c888..f4e4fb8c 100644
--- a/Sources/Domain/Interfaces/UseCases/UserSettingsUseCaseProtocol.swift
+++ b/Sources/Domain/Interfaces/UseCases/UserSettings/UserSettingsUseCaseProtocol.swift
@@ -21,4 +21,6 @@ public protocol UserSettingsUseCaseProtocol {
 
     func offHaptics() -> Single<Void>
 
+    func updateThemeStyle(_ style: ThemeStyle) -> Single<Void>
+
 }
diff --git a/Sources/Domain/Interfaces/UseCases/Word/WordUseCaseError.swift b/Sources/Domain/Interfaces/UseCases/Word/WordUseCaseError.swift
new file mode 100644
index 00000000..37a1d8ef
--- /dev/null
+++ b/Sources/Domain/Interfaces/UseCases/Word/WordUseCaseError.swift
@@ -0,0 +1,41 @@
+//
+//  WordUseCaseError.swift
+//  Domain
+//
+//  Created by Jaewon Yun on 2/12/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import Foundation
+
+public enum WordUseCaseError: Error {
+
+    /// `saveFailed` 에러가 발생한 이유입니다.
+    public enum SaveFailureReason {
+
+        /// 저장하려는 단어가 이미 암기 완료 상태입니다.
+        case wordStateInvalid
+
+        /// 저장하려는 단어가 중복 단어입니다.
+        case duplicatedWord(word: String)
+
+    }
+
+    /// `retrieveFailed` 에러가 발생한 이유입니다.
+    public enum RetrieveFailureReason {
+
+        /// 해당 UUID 와 일치하는 단어가 없습니다.
+        case uuidInvaild(uuid: UUID)
+
+    }
+
+    /// 단어 저장 실패
+    case saveFailed(reason: SaveFailureReason)
+
+    /// 단어 검색 실패
+    case retrieveFailed(reason: RetrieveFailureReason)
+
+    /// 현재 암기중인 단어가 없음
+    case noMemorizingWords
+
+}
diff --git a/Sources/Domain/Interfaces/UseCases/WordUseCaseProtocol.swift b/Sources/Domain/Interfaces/UseCases/Word/WordUseCaseProtocol.swift
similarity index 69%
rename from Sources/Domain/Interfaces/UseCases/WordUseCaseProtocol.swift
rename to Sources/Domain/Interfaces/UseCases/Word/WordUseCaseProtocol.swift
index 958fe3e6..c04d121c 100644
--- a/Sources/Domain/Interfaces/UseCases/WordUseCaseProtocol.swift
+++ b/Sources/Domain/Interfaces/UseCases/Word/WordUseCaseProtocol.swift
@@ -11,6 +11,8 @@ import RxSwift
 public protocol WordUseCaseProtocol {
 
     /// 새 단어를 추가합니다.
+    ///
+    /// - Returns: 단어 추가에 성공하면 Next 이벤트를, 어떠한 이유로 인해 실패하면 `WordUseCaseError` 타입의 Error 이벤트를 방출하는 Sequence 를 반환합니다.
     func addNewWord(_ word: Word) -> Single<Void>
 
     /// 단어를 삭제합니다.
@@ -42,4 +44,9 @@ public protocol WordUseCaseProtocol {
 
     func getCurrentUnmemorizedWord() -> Single<Word>
 
+    /// `word` 파라미터로 전달된 단어가 이미 저장되어 있는 단어인지 검사합니다.
+    ///
+    /// - Returns: 반환된 Sequence 는 `ture` or `false` 값을 가진 next 이벤트만 방출됩니다. error 이벤트는 방출되지 않습니다.
+    func isWordDuplicated(_ word: String) -> Single<Bool>
+
 }
diff --git a/Sources/Domain/UseCases/ExternalStoreUseCase.swift b/Sources/Domain/UseCases/ExternalStoreUseCase.swift
index bef269fd..6383662a 100644
--- a/Sources/Domain/UseCases/ExternalStoreUseCase.swift
+++ b/Sources/Domain/UseCases/ExternalStoreUseCase.swift
@@ -172,11 +172,3 @@ public final class ExternalStoreUseCase: ExternalStoreUseCaseProtocol {
     }
 
 }
-
-enum ExternalStoreUseCaseError: Error {
-
-    case noCurrentUser
-
-    case noPresentingConfiguration
-
-}
diff --git a/Sources/Domain/UseCases/NotificationsUseCase.swift b/Sources/Domain/UseCases/NotificationsUseCase.swift
index de712324..483d476c 100644
--- a/Sources/Domain/UseCases/NotificationsUseCase.swift
+++ b/Sources/Domain/UseCases/NotificationsUseCase.swift
@@ -7,15 +7,11 @@
 //
 
 import Foundation
+import FoundationPlus
 import RxSwift
 import RxUtility
-import Then
 import UserNotifications
 
-enum NotificationsUseCaseError: Error {
-    case noWordsToMemorize
-}
-
 final class NotificationsUseCase: NotificationsUseCaseProtocol {
 
     /// Notification request 의 고유 ID
@@ -59,10 +55,9 @@ final class NotificationsUseCase: NotificationsUseCaseProtocol {
         let setDailyReminderSequence: Single<Void> = .create { observer in
             let unmemorizedWordCount = self.wordRepository.getUnmemorizedList().count
 
-            var content: UNMutableNotificationContent = .init().then {
-                $0.title = DomainString.daily_reminder
-                $0.sound = .default
-            }
+            var content: UNMutableNotificationContent = .init()
+            content.title = DomainString.daily_reminder
+            content.sound = .default
 
             if unmemorizedWordCount == 0 {
                 content.body = DomainString.daily_reminder_body_message_when_no_words_to_memorize
diff --git a/Sources/Domain/UseCases/UserSettingsUseCase.swift b/Sources/Domain/UseCases/UserSettingsUseCase.swift
index 6a130187..1075d24f 100644
--- a/Sources/Domain/UseCases/UserSettingsUseCase.swift
+++ b/Sources/Domain/UseCases/UserSettingsUseCase.swift
@@ -12,11 +12,6 @@ import RxRelay
 import RxUtility
 import Utility
 
-enum UserSettingsUseCaseError: Error {
-    case noPendingDailyReminder
-    case noNotificationAuthorization
-}
-
 public final class UserSettingsUseCase: UserSettingsUseCaseProtocol {
 
     let userSettingsRepository: UserSettingsRepositoryProtocol
@@ -100,10 +95,20 @@ public final class UserSettingsUseCase: UserSettingsUseCaseProtocol {
                     translationTargetLocale = .english
                 }
 
-                let userSettings: UserSettings = .init(translationSourceLocale: .english, translationTargetLocale: translationTargetLocale, hapticsIsOn: true) // FIXME: 처음에 Source Locale 설정 가능하게 (현재 .english 고정)
+                let initialUserSettings: UserSettings = .init(translationSourceLocale: .english, translationTargetLocale: translationTargetLocale, hapticsIsOn: true, themeStyle: .system) // FIXME: 처음에 Source Locale 설정 가능하게 (현재 .english 고정)
+
+                return self.userSettingsRepository.saveUserSettings(initialUserSettings)
+            }
+    }
 
-                return self.userSettingsRepository.saveUserSettings(userSettings)
+    public func updateThemeStyle(_ style: ThemeStyle) -> Single<Void> {
+        return userSettingsRepository.getUserSettings()
+            .map { currentSettings in
+                var newSettings = currentSettings
+                newSettings.themeStyle = style
+                return newSettings
             }
+            .flatMap { self.userSettingsRepository.saveUserSettings($0) }
     }
 
 }
diff --git a/Sources/Domain/UseCases/WordUseCase.swift b/Sources/Domain/UseCases/WordUseCase.swift
index b531b416..9e27a02e 100644
--- a/Sources/Domain/UseCases/WordUseCase.swift
+++ b/Sources/Domain/UseCases/WordUseCase.swift
@@ -23,7 +23,13 @@ public final class WordUseCase: WordUseCaseProtocol {
     public func addNewWord(_ word: Word) -> RxSwift.Single<Void> {
         return .create { single in
             guard word.memorizedState != .memorized else {
-                single(.failure(WordUseCaseError.canNotSaveWord(reason: "Can only add word with a memorization state of `.memorizing`.")))
+                single(.failure(WordUseCaseError.saveFailed(reason: .wordStateInvalid)))
+                return Disposables.create()
+            }
+
+            let allWords = self.wordRepository.getAllWords()
+            if allWords.contains(where: { $0.word.lowercased() == word.word.lowercased() }) {
+                single(.failure(WordUseCaseError.saveFailed(reason: .duplicatedWord(word: word.word))))
                 return Disposables.create()
             }
 
@@ -85,7 +91,7 @@ public final class WordUseCase: WordUseCaseProtocol {
             if let word = self.wordRepository.getWord(by: uuid) {
                 single(.success(word))
             } else {
-                single(.failure(WordUseCaseError.invalidUUID(uuid)))
+                single(.failure(WordUseCaseError.retrieveFailed(reason: .uuidInvaild(uuid: uuid))))
             }
 
             return Disposables.create()
@@ -93,6 +99,15 @@ public final class WordUseCase: WordUseCaseProtocol {
     }
 
     public func updateWord(by uuid: UUID, to newWord: Word) -> RxSwift.Single<Void> {
+        guard let originWord = wordRepository.getWord(by: uuid) else {
+            return .error(WordUseCaseError.retrieveFailed(reason: .uuidInvaild(uuid: uuid)))
+        }
+
+        let allWords = self.wordRepository.getAllWords()
+        if (originWord.word != newWord.word) && allWords.contains(where: { $0.word.lowercased() == newWord.word.lowercased() }) {
+            return .error(WordUseCaseError.saveFailed(reason: .duplicatedWord(word: newWord.word)))
+        }
+
         return .create { single in
             let updateTarget: Word = .init(
                 uuid: uuid,
@@ -151,7 +166,7 @@ public final class WordUseCase: WordUseCaseProtocol {
     public func markCurrentWordAsMemorized(uuid: UUID) -> RxSwift.Single<Void> {
         return .create { single in
             guard let currentWord = self.wordRepository.getWord(by: uuid) else {
-                single(.failure(WordUseCaseError.invalidUUID(uuid)))
+                single(.failure(WordUseCaseError.retrieveFailed(reason: .uuidInvaild(uuid: uuid))))
                 return Disposables.create()
             }
 
@@ -174,17 +189,13 @@ public final class WordUseCase: WordUseCaseProtocol {
         return .just(currentWord)
     }
 
-}
-
-enum WordUseCaseError: Error {
-
-    /// 해당되는 단어가 없는 UUID
-    case invalidUUID(UUID)
-
-    /// 단어를 저장할 수 없음
-    case canNotSaveWord(reason: String)
-
-    /// 현재 암기중인 단어가 없음
-    case noMemorizingWords
+    public func isWordDuplicated(_ word: String) -> Single<Bool> {
+        let allWords = self.wordRepository.getAllWords()
+        if allWords.contains(where: { $0.word.lowercased() == word.lowercased() }) {
+            return .just(true)
+        } else {
+            return .just(false)
+        }
+    }
 
 }
diff --git a/Sources/Domain/ValueObjects/ThemeStyle.swift b/Sources/Domain/ValueObjects/ThemeStyle.swift
new file mode 100644
index 00000000..2306231c
--- /dev/null
+++ b/Sources/Domain/ValueObjects/ThemeStyle.swift
@@ -0,0 +1,21 @@
+//
+//  ThemeStyle.swift
+//  Domain
+//
+//  Created by Jaewon Yun on 2/7/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+/// 적용 가능한 테마 스타일.
+public enum ThemeStyle: Codable {
+
+    /// 시스템 설정을 따르는 스타일
+    case system
+
+    /// Light 스타일
+    case light
+
+    /// Dark 스타일
+    case dark
+
+}
diff --git a/Sources/Domain/ValueObjects/UserSettings.swift b/Sources/Domain/ValueObjects/UserSettings.swift
index 206526ee..3db6ed81 100644
--- a/Sources/Domain/ValueObjects/UserSettings.swift
+++ b/Sources/Domain/ValueObjects/UserSettings.swift
@@ -19,10 +19,14 @@ public struct UserSettings {
     /// 진동 사용 여부
     public var hapticsIsOn: Bool
 
-    public init(translationSourceLocale: TranslationLanguage, translationTargetLocale: TranslationLanguage, hapticsIsOn: Bool) {
+    /// 테마 스타일
+    public var themeStyle: ThemeStyle
+
+    public init(translationSourceLocale: TranslationLanguage, translationTargetLocale: TranslationLanguage, hapticsIsOn: Bool, themeStyle: ThemeStyle) {
         self.translationSourceLocale = translationSourceLocale
         self.translationTargetLocale = translationTargetLocale
         self.hapticsIsOn = hapticsIsOn
+        self.themeStyle = themeStyle
     }
 
 }
diff --git a/Sources/DomainTesting/UserSettingsUseCaseFake.swift b/Sources/DomainTesting/UserSettingsUseCaseFake.swift
index 01d05eca..7ffbf7ed 100644
--- a/Sources/DomainTesting/UserSettingsUseCaseFake.swift
+++ b/Sources/DomainTesting/UserSettingsUseCaseFake.swift
@@ -16,7 +16,8 @@ public final class UserSettingsUseCaseFake: UserSettingsUseCaseProtocol {
     public var currentUserSettings: Domain.UserSettings = .init(
         translationSourceLocale: .english,
         translationTargetLocale: .korean,
-        hapticsIsOn: true
+        hapticsIsOn: true,
+        themeStyle: .system
     )
 
     public init() {}
@@ -48,4 +49,9 @@ public final class UserSettingsUseCaseFake: UserSettingsUseCaseProtocol {
         return .just(())
     }
 
+    public func updateThemeStyle(_ style: ThemeStyle) -> Single<Void> {
+        currentUserSettings.themeStyle = style
+        return .just(())
+    }
+
 }
diff --git a/Sources/DomainTesting/WordUseCaseFake.swift b/Sources/DomainTesting/WordUseCaseFake.swift
index f4c800c3..858de266 100644
--- a/Sources/DomainTesting/WordUseCaseFake.swift
+++ b/Sources/DomainTesting/WordUseCaseFake.swift
@@ -15,6 +15,7 @@ import Utility
 
 public final class WordUseCaseFake: WordUseCaseProtocol {
 
+    /// Fake 객체 구현을 위해 사용한 인메모리 단어 저장소
     public var _wordList: [Domain.Word] = []
 
     public var _unmemorizedWordList: UnmemorizedWordListRepositorySpy = .init()
@@ -22,6 +23,10 @@ public final class WordUseCaseFake: WordUseCaseProtocol {
     public init() {}
 
     public func addNewWord(_ word: Domain.Word) -> Single<Void> {
+        if _wordList.contains(where: { $0.word.lowercased() == word.word.lowercased() }) {
+            return .error(WordUseCaseError.saveFailed(reason: .duplicatedWord(word: word.word)))
+        }
+
         _wordList.append(word)
         _unmemorizedWordList.addWord(word)
         return .just(())
@@ -51,16 +56,39 @@ public final class WordUseCaseFake: WordUseCaseProtocol {
 
     public func getWord(by uuid: UUID) -> Single<Domain.Word> {
         guard let word = _wordList.first(where: { $0.uuid == uuid }) else {
-            return .error(WordUseCaseError.invalidUUID(uuid))
+            return .error(WordUseCaseError.retrieveFailed(reason: .uuidInvaild(uuid: uuid)))
         }
         return .just(word)
     }
 
     public func updateWord(by uuid: UUID, to newWord: Domain.Word) -> Single<Void> {
-        if let index = _wordList.firstIndex(where: { $0.uuid == uuid }) {
-            _wordList[index] = newWord
+        guard let index = _wordList.firstIndex(where: { $0.uuid == uuid }) else {
+            return .error(WordUseCaseError.retrieveFailed(reason: .uuidInvaild(uuid: uuid)))
         }
-        _unmemorizedWordList.replaceWord(where: uuid, with: newWord)
+
+        if (newWord.word != _wordList[index].word) && _wordList.contains(where: { $0.word.lowercased() == newWord.word.lowercased() }) {
+            return .error(WordUseCaseError.saveFailed(reason: .duplicatedWord(word: newWord.word)))
+        }
+
+        let updateTarget: Word = .init(
+            uuid: uuid,
+            word: newWord.word,
+            memorizedState: newWord.memorizedState
+        )
+
+        if _unmemorizedWordList.contains(where: { $0.uuid == updateTarget.uuid }) {
+            switch updateTarget.memorizedState {
+            case .memorized:
+                _unmemorizedWordList.deleteWord(by: uuid)
+            case .memorizing:
+                _unmemorizedWordList.replaceWord(where: uuid, with: updateTarget)
+            }
+        } else if updateTarget.memorizedState == .memorizing {
+            _unmemorizedWordList.addWord(updateTarget)
+        }
+
+        _wordList[index] = updateTarget
+
         return .just(())
     }
 
@@ -97,4 +125,12 @@ public final class WordUseCaseFake: WordUseCaseProtocol {
         return .just(currentWord)
     }
 
+    public func isWordDuplicated(_ word: String) -> Single<Bool> {
+        if _wordList.contains(where: { $0.word.lowercased() == word.lowercased() }) {
+            return .just(true)
+        } else {
+            return .just(false)
+        }
+    }
+
 }
diff --git a/Sources/FoundationExtension/AllCases+index.swift b/Sources/FoundationExtension/AllCases+index.swift
deleted file mode 100644
index 9f129706..00000000
--- a/Sources/FoundationExtension/AllCases+index.swift
+++ /dev/null
@@ -1,23 +0,0 @@
-//
-//  AllCases+index.swift
-//  iOSSupport
-//
-//  Created by Jaewon Yun on 2/5/24.
-//  Copyright © 2024 woin2ee. All rights reserved.
-//
-
-import Foundation
-
-extension Array where Element: CaseIterable & Equatable {
-
-    /// AllCases 배열에서 주어진 열거형 값에 해당하는 index 를 반환합니다.
-    /// - Parameter element: 열거형 값
-    /// - Returns: 주어진 열거형 값에 해당하는 index
-    public func index(of element: Element) -> Int {
-        guard let index = self.firstIndex(of: element) else {
-            fatalError("This method was used where it was not appropriate.")
-        }
-        return index
-    }
-
-}
diff --git a/Sources/FoundationExtension/Collection+isNotEmpty.swift b/Sources/FoundationExtension/Collection+isNotEmpty.swift
deleted file mode 100644
index 3f0c91e6..00000000
--- a/Sources/FoundationExtension/Collection+isNotEmpty.swift
+++ /dev/null
@@ -1,16 +0,0 @@
-//
-//  Collection+isNotEmpty.swift
-//  ItsME
-//
-//  Created by Jaewon Yun on 2023/03/24.
-//
-
-import Foundation
-
-extension Collection {
-
-    /// A Boolean value indicating whether the collection is not empty.
-    public var isNotEmpty: Bool {
-        !isEmpty
-    }
-}
diff --git a/Sources/iPhoneDriver/iPhoneAppDelegate.swift b/Sources/IPhoneDriver/IPhoneAppDelegate.swift
similarity index 89%
rename from Sources/iPhoneDriver/iPhoneAppDelegate.swift
rename to Sources/IPhoneDriver/IPhoneAppDelegate.swift
index 842e0c59..195835fb 100644
--- a/Sources/iPhoneDriver/iPhoneAppDelegate.swift
+++ b/Sources/IPhoneDriver/IPhoneAppDelegate.swift
@@ -1,5 +1,5 @@
 //
-//  iPhoneAppDelegate.swift
+//  IPhoneAppDelegate.swift
 //  iPhoneDriver
 //
 //  Created by Jaewon Yun on 1/30/24.
@@ -7,25 +7,30 @@
 //
 
 import Domain
-import GeneralSettings
 import GoogleSignIn
 import Infrastructure
-import iOSSupport
-import LanguageSetting
-import PushNotificationSettings
+import IOSSupport
 import RxSwift
-import Swinject
-import SwinjectDIContainer
 import UIKit
-import UserSettings
 import Utility
+
+// Scenes
+import GeneralSettings
+import LanguageSetting
+import PushNotificationSettings
+import ThemeSetting
+import UserSettings
 import WordAddition
 import WordChecking
 import WordDetail
 import WordList
 
+// DI
+import Swinject
+import SwinjectDIContainer
+
 // swiftlint:disable type_name
-open class iPhoneAppDelegate: UIResponder, UIApplicationDelegate {
+open class IPhoneAppDelegate: UIResponder, UIApplicationDelegate {
 
     public func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
         initDIContainer()
@@ -90,21 +95,23 @@ open class iPhoneAppDelegate: UIResponder, UIApplicationDelegate {
             LanguageSettingAssembly(),
             PushNotificationSettingsAssembly(),
             GeneralSettingsAssembly(),
+            ThemeSettingAssembly(),
         ])
     }
 
     func initGlobalState() {
         let userSettingsUseCase: UserSettingsUseCaseProtocol = DIContainer.shared.resolver.resolve()
         _ = userSettingsUseCase.getCurrentUserSettings()
-            .map(\.hapticsIsOn)
-            .doOnSuccess(GlobalState.shared.initialize)
+            .doOnSuccess {
+                GlobalState.shared.initialize(hapticsIsOn: $0.hapticsIsOn, themeStyle: $0.themeStyle.toUIKit())
+            }
             .subscribe(on: ConcurrentMainScheduler.instance)
             .subscribe()
     }
 
 }
 
-extension iPhoneAppDelegate: UNUserNotificationCenterDelegate {
+extension IPhoneAppDelegate: UNUserNotificationCenterDelegate {
 
     public func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse) async {
         RootTabBarController.shared.selectedViewController = RootTabBarController.shared.wordCheckingNC
diff --git a/Sources/Infrastructure/DI/UserSettingsRepositoryAssemblyDev.swift b/Sources/Infrastructure/DI/UserSettingsRepositoryAssemblyDev.swift
index 8636b424..8f84e304 100644
--- a/Sources/Infrastructure/DI/UserSettingsRepositoryAssemblyDev.swift
+++ b/Sources/Infrastructure/DI/UserSettingsRepositoryAssemblyDev.swift
@@ -17,8 +17,10 @@ final class UserSettingsRepositoryAssemblyDev: Assembly {
     func assemble(container: Container) {
         container.register(UserSettingsRepositoryProtocol.self) { _ in
             let userDefaults: ExtendedUserDefaults = .init(suiteName: "Dev")!
-            let arguments = ProcessInfo.processInfo.arguments
-            if arguments.contains(LaunchArguments.initUserDefaults.rawValue) {
+
+            LaunchArgument.verify()
+
+            if LaunchArgument.contains(.initUserDefaults) {
                 userDefaults.removeAllObject(forKeyType: UserDefaultsKey.self)
             }
 
diff --git a/Sources/Infrastructure/DI/WordRepositoryAssemblyDev.swift b/Sources/Infrastructure/DI/WordRepositoryAssemblyDev.swift
index ae185c13..303a5af9 100644
--- a/Sources/Infrastructure/DI/WordRepositoryAssemblyDev.swift
+++ b/Sources/Infrastructure/DI/WordRepositoryAssemblyDev.swift
@@ -16,14 +16,16 @@ final class WordRepositoryAssemblyDev: Assembly {
 
     func assemble(container: Container) {
         container.register(WordRepositoryProtocol.self) { _ in
-            let arguments = ProcessInfo.processInfo.arguments
-            // TODO: Insert [LaunchArguments 검증 code](상호배타적인것들)
-            if arguments.contains(LaunchArguments.useInMemoryDatabase.rawValue) {
+            LaunchArgument.verify()
+
+            if LaunchArgument.contains(.useInMemoryDatabase) {
                 return self.makeInMemoryWordRepository()
             }
-            if arguments.contains(LaunchArguments.sampledDatabase.rawValue) {
+
+            if LaunchArgument.contains(.sampledDatabase) {
                 return self.makeSampledWordRepository()
             }
+
             return self.makePersistenceWordRepository()
         }
         .inObjectScope(.container)
diff --git a/Sources/Infrastructure/DomainImpl/UserSettingsRepository.swift b/Sources/Infrastructure/DomainImpl/UserSettingsRepository.swift
index 42655bff..8c78072c 100644
--- a/Sources/Infrastructure/DomainImpl/UserSettingsRepository.swift
+++ b/Sources/Infrastructure/DomainImpl/UserSettingsRepository.swift
@@ -31,7 +31,8 @@ final class UserSettingsRepository: UserSettingsRepositoryProtocol {
                 userSettings.translationTargetLocale,
                 forKey: UserDefaultsKey.translationTargetLocale
             ),
-            userDefaults.rx.setValue(userSettings.hapticsIsOn, forKey: UserDefaultsKey.hapticsIsOn)
+            userDefaults.rx.setValue(userSettings.hapticsIsOn, forKey: UserDefaultsKey.hapticsIsOn),
+            userDefaults.rx.setCodable(userSettings.themeStyle, forKey: UserDefaultsKey.themeStyle)
         )
         .mapToVoid()
     }
@@ -40,13 +41,15 @@ final class UserSettingsRepository: UserSettingsRepositoryProtocol {
         return Single.zip(
             userDefaults.rx.object(TranslationLanguage.self, forKey: UserDefaultsKey.translationSourceLocale),
             userDefaults.rx.object(TranslationLanguage.self, forKey: UserDefaultsKey.translationTargetLocale),
-            userDefaults.rx.bool(forKey: UserDefaultsKey.hapticsIsOn)
+            userDefaults.rx.bool(forKey: UserDefaultsKey.hapticsIsOn),
+            userDefaults.rx.object(ThemeStyle.self, forKey: UserDefaultsKey.themeStyle)
         )
-        .map { sourceLocale, targetLocale, hapticsIsOn -> Domain.UserSettings in
+        .map { sourceLocale, targetLocale, hapticsIsOn, themeStyle -> Domain.UserSettings in
             return .init(
                 translationSourceLocale: sourceLocale,
                 translationTargetLocale: targetLocale,
-                hapticsIsOn: hapticsIsOn
+                hapticsIsOn: hapticsIsOn,
+                themeStyle: themeStyle
             )
         }
     }
diff --git a/Sources/Infrastructure/UserDefaults/UserDefaultsKey.swift b/Sources/Infrastructure/UserDefaults/UserDefaultsKey.swift
index 322a6ca8..99dfbcc0 100644
--- a/Sources/Infrastructure/UserDefaults/UserDefaultsKey.swift
+++ b/Sources/Infrastructure/UserDefaults/UserDefaultsKey.swift
@@ -19,6 +19,8 @@ enum UserDefaultsKey: UserDefaultsKeyProtocol, CaseIterable {
 
     case hapticsIsOn
 
+    case themeStyle
+
     /// 테스트용 Key 입니다.
     case test
 
diff --git a/Sources/Utility/Concurrency/Sequence+asyncForEach.swift b/Sources/Utility/Concurrency/Sequence+asyncForEach.swift
deleted file mode 100644
index 39143c4b..00000000
--- a/Sources/Utility/Concurrency/Sequence+asyncForEach.swift
+++ /dev/null
@@ -1,19 +0,0 @@
-//
-//  Sequence+asyncForEach.swift
-//  iOSCore
-//
-//  Created by Jaewon Yun on 2023/10/06.
-//  Copyright © 2023 woin2ee. All rights reserved.
-//
-
-import Foundation
-
-extension Sequence {
-
-    public func asyncForEach(_ body: (Self.Element) async throws -> Void) async rethrows {
-        for element in self {
-            try await body(element)
-        }
-    }
-
-}
diff --git a/Sources/Utility/Concurrency/Task+.swift b/Sources/Utility/Concurrency/Task+.swift
deleted file mode 100644
index 0bce10bb..00000000
--- a/Sources/Utility/Concurrency/Task+.swift
+++ /dev/null
@@ -1,28 +0,0 @@
-//
-//  Task+.swift
-//  iOSCore
-//
-//  Created by Jaewon Yun on 2023/10/06.
-//  Copyright © 2023 woin2ee. All rights reserved.
-//
-
-import Foundation
-
-extension Task where Success == Void, Failure == Never {
-
-    @discardableResult
-    public init(
-        priority: TaskPriority? = nil,
-        operation: @escaping (() async throws -> Void),
-        catch: @escaping ((Error) -> Void)
-    ) {
-        self.init(priority: priority) {
-            do {
-                try await operation()
-            } catch {
-                `catch`(error)
-            }
-        }
-    }
-
-}
diff --git a/Sources/Utility/LaunchArgument.swift b/Sources/Utility/LaunchArgument.swift
new file mode 100644
index 00000000..ceda59b8
--- /dev/null
+++ b/Sources/Utility/LaunchArgument.swift
@@ -0,0 +1,45 @@
+//
+//  LaunchArgument.swift
+//  WordChecker
+//
+//  Created by Jaewon Yun on 2023/08/27.
+//
+
+import Foundation
+
+public final class LaunchArgument {
+
+    private init() {}
+
+    /// 사용 가능한 launch argument 목록입니다.
+    public enum Arguments: String {
+
+        /// 인메모리 데이터베이스를 사용합니다.
+        case useInMemoryDatabase = "-useInMemoryDatabase"
+
+        /// 샘플 데이터를 적용합니다.
+        case sampledDatabase = "-sampledDatabase"
+
+        /// UserDefaults 를 초기화합니다.
+        case initUserDefaults = "-initUserDefaults"
+
+    }
+
+    public static func contains(_ launchArguments: Arguments) -> Bool {
+        let arguments = ProcessInfo.processInfo.arguments
+        return arguments.contains(launchArguments.rawValue)
+    }
+
+    public static func contains(_ launchArguments: String) -> Bool {
+        let arguments = ProcessInfo.processInfo.arguments
+        return arguments.contains(launchArguments)
+    }
+
+    /// Launch arguments 가 올바르게 적용되었는지 검증합니다.
+    public static func verify() {
+        if self.contains(.useInMemoryDatabase) && self.contains(.sampledDatabase) {
+            fatalError("\(Arguments.useInMemoryDatabase) and \(Arguments.sampledDatabase) should not be used together.")
+        }
+    }
+
+}
diff --git a/Sources/Utility/LaunchArguments.swift b/Sources/Utility/LaunchArguments.swift
deleted file mode 100644
index 0343eea9..00000000
--- a/Sources/Utility/LaunchArguments.swift
+++ /dev/null
@@ -1,18 +0,0 @@
-//
-//  LaunchArguments.swift
-//  WordChecker
-//
-//  Created by Jaewon Yun on 2023/08/27.
-//
-
-import Foundation
-
-public enum LaunchArguments: String {
-
-    case useInMemoryDatabase = "-useInMemoryDatabase"
-
-    case sampledDatabase = "-sampledDatabase"
-
-    case initUserDefaults = "-initUserDefaults"
-
-}
diff --git a/Sources/WordChecker/AppDelegate.swift b/Sources/WordChecker/AppDelegate.swift
index d56f43d0..166e3df6 100644
--- a/Sources/WordChecker/AppDelegate.swift
+++ b/Sources/WordChecker/AppDelegate.swift
@@ -5,8 +5,8 @@
 //  Created by Jaewon Yun on 2023/08/23.
 //
 
-import iPhoneDriver
+import IPhoneDriver
 
 @main
-class AppDelegate: iPhoneAppDelegate {
+class AppDelegate: IPhoneAppDelegate {
 }
diff --git a/Sources/WordCheckerDev/AppDelegate.swift b/Sources/WordCheckerDev/AppDelegate.swift
index e03d50cf..2b532165 100644
--- a/Sources/WordCheckerDev/AppDelegate.swift
+++ b/Sources/WordCheckerDev/AppDelegate.swift
@@ -6,13 +6,14 @@
 //
 
 import Domain
-import iPhoneDriver
+import IPhoneDriver
 import Infrastructure
 
 // Scenes
 import GeneralSettings
 import LanguageSetting
 import PushNotificationSettings
+import ThemeSetting
 import UserSettings
 import WordAddition
 import WordChecking
@@ -24,7 +25,7 @@ import Swinject
 import SwinjectDIContainer
 
 @main
-class AppDelegate: iPhoneAppDelegate {
+class AppDelegate: IPhoneAppDelegate {
 
     override func restoreGoogleSignInState() {
         // No restore for dev.
@@ -42,6 +43,7 @@ class AppDelegate: iPhoneAppDelegate {
             LanguageSettingAssembly(),
             PushNotificationSettingsAssemblyDev(),
             GeneralSettingsAssembly(),
+            ThemeSettingAssembly(),
         ])
     }
 
diff --git a/Sources/iOSScenes/GeneralSettings/GeneralSettingsReactor.swift b/Sources/iOSScenes/GeneralSettings/GeneralSettingsReactor.swift
index f53e993b..c64273a1 100644
--- a/Sources/iOSScenes/GeneralSettings/GeneralSettingsReactor.swift
+++ b/Sources/iOSScenes/GeneralSettings/GeneralSettingsReactor.swift
@@ -7,7 +7,7 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
 final class GeneralSettingsReactor: Reactor {
diff --git a/Sources/iOSScenes/GeneralSettings/GeneralSettingsViewController.swift b/Sources/iOSScenes/GeneralSettings/GeneralSettingsViewController.swift
index ab030be2..8db35b03 100644
--- a/Sources/iOSScenes/GeneralSettings/GeneralSettingsViewController.swift
+++ b/Sources/iOSScenes/GeneralSettings/GeneralSettingsViewController.swift
@@ -6,14 +6,14 @@
 //  Copyright © 2024 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import RxUtility
 import Then
 import UIKit
 
-public protocol GeneralSettingsViewControllerDelegate: AnyObject {
-    func willPopView()
+public protocol GeneralSettingsViewControllerDelegate: AnyObject, ViewControllerDelegate {
+    func didTapThemeSetting()
 }
 
 public protocol GeneralSettingsViewControllerProtocol: UIViewController {
@@ -24,16 +24,19 @@ final class GeneralSettingsViewController: RxBaseViewController, View, GeneralSe
 
     enum SectionIdentifier: Int {
         case hapticsSettings = 0
+        case themeSetting
     }
 
     enum ItemIdentifier {
         case hapticsOnOffSwitch
+        case themeSetting
     }
 
     weak var delegate: GeneralSettingsViewControllerDelegate?
 
     lazy var rootView: UITableView = .init(frame: .zero, style: .insetGrouped).then {
         $0.registerCell(ManualSwitchCell.self)
+        $0.registerCell(DisclosureIndicatorCell.self)
         $0.registerHeaderFooterView(TextFooterView.self)
         $0.delegate = self
     }
@@ -60,6 +63,11 @@ final class GeneralSettingsViewController: RxBaseViewController, View, GeneralSe
                 .bind(to: reactor.action)
                 .disposed(by: cell.disposeBag)
             return cell
+
+        case .themeSetting:
+            let cell = tableView.dequeueReusableCell(DisclosureIndicatorCell.self, for: indexPath)
+            cell.bind(model: .init(title: WCString.theme))
+            return cell
         }
     }
 
@@ -78,21 +86,37 @@ final class GeneralSettingsViewController: RxBaseViewController, View, GeneralSe
         applyInitialSnapshot()
     }
 
-    override func viewWillDisappear(_ animated: Bool) {
-        super.viewWillDisappear(animated)
+    override func viewDidDisappear(_ animated: Bool) {
+        super.viewDidDisappear(animated)
 
         if self.isMovingFromParent {
-            delegate?.willPopView()
+            delegate?.viewControllerDidPop(self)
         }
     }
 
     func applyInitialSnapshot() {
         var snapshot = dataSource.snapshot()
-        snapshot.appendSections([.hapticsSettings])
+        snapshot.appendSections([
+            .hapticsSettings,
+            .themeSetting,
+        ])
         snapshot.appendItems([.hapticsOnOffSwitch], toSection: .hapticsSettings)
+        snapshot.appendItems([.themeSetting], toSection: .themeSetting)
         dataSource.applySnapshotUsingReloadData(snapshot)
     }
 
+    override func bindAction() {
+        let itemSelectedEvent = rootView.rx.itemSelected.asSignal()
+            .doOnNext { [weak self] in self?.rootView.deselectRow(at: $0, animated: true) }
+
+        itemSelectedEvent
+            .filter { self.dataSource.itemIdentifier(for: $0) == .themeSetting }
+            .emit(with: self, onNext: { owner, _ in
+                owner.delegate?.didTapThemeSetting()
+            })
+            .disposed(by: self.disposeBag)
+    }
+
     func bind(reactor: GeneralSettingsReactor) {
         // Action
         self.rx.sentMessage(#selector(viewDidLoad))
diff --git a/Sources/iOSScenes/LanguageSetting/LanguageSettingReactor.swift b/Sources/iOSScenes/LanguageSetting/LanguageSettingReactor.swift
index b750a9b3..93770e5f 100644
--- a/Sources/iOSScenes/LanguageSetting/LanguageSettingReactor.swift
+++ b/Sources/iOSScenes/LanguageSetting/LanguageSettingReactor.swift
@@ -8,8 +8,8 @@
 
 import Domain
 import Foundation
-import FoundationExtension
-import iOSSupport
+import FoundationPlus
+import IOSSupport
 import ReactorKit
 
 final class LanguageSettingReactor: Reactor {
@@ -32,12 +32,12 @@ final class LanguageSettingReactor: Reactor {
 
     let userSettingsUseCase: UserSettingsUseCaseProtocol
 
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
 
     init(
         translationDirection: TranslationDirection,
         userSettingsUseCase: UserSettingsUseCaseProtocol,
-        globalAction: GlobalReactorAction
+        globalAction: GlobalAction
     ) {
         self.initialState = .init(translationDirection: translationDirection, selectedCell: .init())
         self.userSettingsUseCase = userSettingsUseCase
diff --git a/Sources/iOSScenes/LanguageSetting/LanguageSettingViewController.swift b/Sources/iOSScenes/LanguageSetting/LanguageSettingViewController.swift
index 4113d44f..ffe4085a 100644
--- a/Sources/iOSScenes/LanguageSetting/LanguageSettingViewController.swift
+++ b/Sources/iOSScenes/LanguageSetting/LanguageSettingViewController.swift
@@ -7,19 +7,15 @@
 //
 
 import Domain
-import FoundationExtension
-import iOSSupport
+import FoundationPlus
+import IOSSupport
 import OrderedCollections
 import ReactorKit
 import RxSwift
 import Then
 import UIKit
 
-public protocol LanguageSettingViewControllerDelegate: AnyObject {
-
-    /// ViewController 가 Pop 해야될때 호출되는 Delegate method 입니다.
-    func viewMustPop()
-
+public protocol LanguageSettingViewControllerDelegate: AnyObject, ViewControllerDelegate {
 }
 
 public protocol LanguageSettingViewControllerProtocol: UIViewController {
@@ -95,16 +91,16 @@ final class LanguageSettingViewController: RxBaseViewController, LanguageSetting
         applyInitialSnapshotIfNoSections()
     }
 
-    override func viewDidDisappear(_ animated: Bool) {
-        super.viewDidDisappear(animated)
+    override func viewWillDisappear(_ animated: Bool) {
+        super.viewWillDisappear(animated)
 
         if self.isMovingFromParent {
-            delegate?.viewMustPop()
+            delegate?.viewControllerDidPop(self)
         }
     }
 
-    /// 현재 Snapshot 에 추가된 Section 이 없다면 초기 snapshot 을 적용합니다.
-    /// - Returns: 현재 Snapshot 에 추가된 Section 이 있다면 현재 snapshot 을 반환, 없다면 새로 적용한 snapshot 을 반환합니다.
+    /// 현재 DataSource 에 적용된 Snapshot 이 없다면 초기 Snapshot 을 적용합니다.
+    /// - Returns: 현재 DataSource 에 적용된 Snapshot 이 있다면 해당 Snapshot 을 반환, 없다면 새로 적용한 Snapshot 을 반환합니다.
     @discardableResult
     func applyInitialSnapshotIfNoSections() -> NSDiffableDataSourceSnapshot<SectionIdentifier, ItemIdentifier> {
         let currenetSnapshot = dataSource.snapshot()
@@ -144,13 +140,14 @@ final class LanguageSettingViewController: RxBaseViewController, LanguageSetting
                 var snapshot = owner.dataSource.snapshot()
                 snapshot = owner.applyInitialSnapshotIfNoSections()
 
-                guard let sectionIdentifier = SectionIdentifier.init(rawValue: selectedIndexPath.section) else {
+                guard
+                    let selectedSectionIdentifier = SectionIdentifier.init(rawValue: selectedIndexPath.section),
+                    let selectedItemIdentifier = owner.dataSource.itemIdentifier(for: selectedIndexPath)
+                else {
                     assertionFailure("Out of selectable cell.")
                     return
                 }
 
-                let selectedItemIdentifier = snapshot.itemIdentifiers(inSection: sectionIdentifier)[selectedIndexPath.row]
-
                 if case .language = selectedItemIdentifier {
                     owner.itemModels = owner.defaultItemModels
                     var selectedItem = owner.itemModels[selectedItemIdentifier]
@@ -158,7 +155,7 @@ final class LanguageSettingViewController: RxBaseViewController, LanguageSetting
                     owner.itemModels[selectedItemIdentifier] = selectedItem
                 }
 
-                snapshot.reconfigureItems(snapshot.itemIdentifiers(inSection: sectionIdentifier))
+                snapshot.reconfigureItems(snapshot.itemIdentifiers(inSection: selectedSectionIdentifier))
                 owner.dataSource.apply(snapshot)
             }
             .disposed(by: self.disposeBag)
diff --git a/Sources/iOSScenes/PushNotificationSettings/Cells/DatePickerCell.swift b/Sources/iOSScenes/PushNotificationSettings/Cells/DatePickerCell.swift
index 6834bea8..0c31dc58 100644
--- a/Sources/iOSScenes/PushNotificationSettings/Cells/DatePickerCell.swift
+++ b/Sources/iOSScenes/PushNotificationSettings/Cells/DatePickerCell.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import UIKit
 
 final class DatePickerCell: RxBaseReusableCell {
diff --git a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsReactor.swift b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsReactor.swift
index 75447f1f..9bb9c048 100644
--- a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsReactor.swift
+++ b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsReactor.swift
@@ -8,7 +8,7 @@
 
 import Domain
 import Foundation
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
 final class PushNotificationSettingsReactor: Reactor {
@@ -40,9 +40,9 @@ final class PushNotificationSettingsReactor: Reactor {
     )
 
     let notificationsUseCase: NotificationsUseCaseProtocol
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
 
-    init(notificationsUseCase: NotificationsUseCaseProtocol, globalAction: GlobalReactorAction) {
+    init(notificationsUseCase: NotificationsUseCaseProtocol, globalAction: GlobalAction) {
         self.notificationsUseCase = notificationsUseCase
         self.globalAction = globalAction
     }
diff --git a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsView.swift b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsView.swift
index fc5580a9..2eafe11e 100644
--- a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsView.swift
+++ b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsView.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import Then
 import UIKit
 
diff --git a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsViewController.swift b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsViewController.swift
index 47220865..2e9884a9 100644
--- a/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsViewController.swift
+++ b/Sources/iOSScenes/PushNotificationSettings/PushNotificationSettingsViewController.swift
@@ -1,10 +1,9 @@
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import Then
 import UIKit
 
-public protocol PushNotificationSettingsDelegate: AnyObject {
-    func willPopView()
+public protocol PushNotificationSettingsDelegate: AnyObject, ViewControllerDelegate {
 }
 
 public protocol PushNotificationSettingsViewControllerProtocol: UIViewController {
@@ -96,11 +95,11 @@ class PushNotificationSettingsViewController: RxBaseViewController, View, PushNo
         isViewAppeared = true
     }
 
-    override func viewWillDisappear(_ animated: Bool) {
-        super.viewWillDisappear(animated)
+    override func viewDidDisappear(_ animated: Bool) {
+        super.viewDidDisappear(animated)
 
         if self.isMovingFromParent {
-            delegate?.willPopView()
+            delegate?.viewControllerDidPop(self)
         }
     }
 
diff --git a/Sources/iOSScenes/PushNotificationSettingsExample/AppDelegate.swift b/Sources/iOSScenes/PushNotificationSettingsExample/AppDelegate.swift
index c494e4a8..66305b16 100644
--- a/Sources/iOSScenes/PushNotificationSettingsExample/AppDelegate.swift
+++ b/Sources/iOSScenes/PushNotificationSettingsExample/AppDelegate.swift
@@ -5,14 +5,13 @@
 //  Created by Jaewon Yun on 2023/08/23.
 //
 
-import iOSSupport
+import IOSSupport
 import UIKit
 
 @main
 class AppDelegate: UIResponder, UIApplicationDelegate {
 
     func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
-        GlobalState.shared.initialize(hapticsIsOn: true)
         return true
     }
 
diff --git a/Sources/iOSScenes/ThemeSetting/ThemeSettingAssembly.swift b/Sources/iOSScenes/ThemeSetting/ThemeSettingAssembly.swift
new file mode 100644
index 00000000..1a78b6d0
--- /dev/null
+++ b/Sources/iOSScenes/ThemeSetting/ThemeSettingAssembly.swift
@@ -0,0 +1,24 @@
+import Swinject
+import SwinjectExtension
+import Then
+
+public final class ThemeSettingAssembly: Assembly {
+
+    public init() {}
+
+    public func assemble(container: Container) {
+        container.register(ThemeSettingReactor.self) { resolver in
+            return ThemeSettingReactor.init(
+                userSettingsUseCase: resolver.resolve(),
+                globalState: .shared
+            )
+        }
+
+        container.register(ThemeSettingViewControllerProtocol.self) { resolver in
+            return ThemeSettingViewController().then {
+                $0.reactor = resolver.resolve()
+            }
+        }
+    }
+
+}
diff --git a/Sources/iOSScenes/ThemeSetting/ThemeSettingReactor.swift b/Sources/iOSScenes/ThemeSetting/ThemeSettingReactor.swift
new file mode 100644
index 00000000..8b15ef38
--- /dev/null
+++ b/Sources/iOSScenes/ThemeSetting/ThemeSettingReactor.swift
@@ -0,0 +1,61 @@
+import Domain
+import IOSSupport
+import ReactorKit
+import UIKit
+
+final class ThemeSettingReactor: Reactor {
+
+    enum Action {
+        case viewDidLoad
+        case selectStyle(UIUserInterfaceStyle)
+    }
+
+    enum Mutation {
+        case setStyle(UIUserInterfaceStyle)
+    }
+
+    struct State {
+        var selectedStyle: UIUserInterfaceStyle
+    }
+
+    var initialState: State = .init(selectedStyle: .unspecified)
+
+    let userSettingsUseCase: UserSettingsUseCaseProtocol
+    let globalState: GlobalState
+
+    init(userSettingsUseCase: UserSettingsUseCaseProtocol, globalState: GlobalState) {
+        self.userSettingsUseCase = userSettingsUseCase
+        self.globalState = globalState
+    }
+
+    func mutate(action: Action) -> Observable<Mutation> {
+        switch action {
+        case .viewDidLoad:
+            return userSettingsUseCase.getCurrentUserSettings()
+                .asObservable()
+                .map(\.themeStyle)
+                .map { $0.toUIKit() }
+                .map(Mutation.setStyle)
+
+        case .selectStyle(let selectedStyle):
+            return userSettingsUseCase.updateThemeStyle(selectedStyle.toDomain())
+                .asObservable()
+                .doOnNext {
+                    self.globalState.themeStyle.accept(selectedStyle)
+                }
+                .map { Mutation.setStyle(selectedStyle) }
+        }
+    }
+
+    func reduce(state: State, mutation: Mutation) -> State {
+        var state = state
+
+        switch mutation {
+        case .setStyle(let selectedStyle):
+            state.selectedStyle = selectedStyle
+        }
+
+        return state
+    }
+
+}
diff --git a/Sources/iOSScenes/ThemeSetting/ThemeSettingViewController.swift b/Sources/iOSScenes/ThemeSetting/ThemeSettingViewController.swift
new file mode 100644
index 00000000..6947532f
--- /dev/null
+++ b/Sources/iOSScenes/ThemeSetting/ThemeSettingViewController.swift
@@ -0,0 +1,152 @@
+import FoundationPlus
+import IOSSupport
+import OrderedCollections
+import ReactorKit
+import UIKit
+
+public protocol ThemeSettingViewControllerDelegate: AnyObject, ViewControllerDelegate {
+}
+
+public protocol ThemeSettingViewControllerProtocol: UIViewController {
+    var delegate: ThemeSettingViewControllerDelegate? { get set }
+}
+
+final class ThemeSettingViewController: RxBaseViewController, View, ThemeSettingViewControllerProtocol {
+
+    enum SectionIdentifier {
+        case theme
+    }
+
+    enum ItemIdentifier: Hashable {
+        case theme(UIUserInterfaceStyle)
+    }
+
+    /// `ItemIdentifier` 로 인해 구분되는 Item 들을 보여주기 위한 값을 가지고 있는 OrderedDictionary 타입 Model 입니다.
+    ///
+    /// `TableView` 에 보여지는 순서대로 값을 가지고 있습니다.
+    lazy var itemModels: OrderedDictionary<ItemIdentifier, CheckmarkCell.Model> = defaultItemModels
+
+    var defaultItemModels: OrderedDictionary<ItemIdentifier, CheckmarkCell.Model> {
+        [
+            ItemIdentifier.theme(.unspecified),
+            ItemIdentifier.theme(.light),
+            ItemIdentifier.theme(.dark),
+        ]
+            .reduce(into: OrderedDictionary<ItemIdentifier, CheckmarkCell.Model>()) { partialResult, itemIdentifier in
+                if case let .theme(style) = itemIdentifier {
+                    partialResult[itemIdentifier] = .init(title: localizedCellTitle(by: style), isChecked: false)
+                }
+            }
+    }
+
+    lazy var dataSource: UITableViewDiffableDataSource<SectionIdentifier, ItemIdentifier> = .init(tableView: rootView) { [weak self] tableView, indexPath, itemIdentifier -> UITableViewCell? in
+        guard let self = self else { return nil }
+        guard let itemModel = itemModels[itemIdentifier] else { return nil }
+
+        switch itemIdentifier {
+        case .theme(let style):
+            let cell = tableView.dequeueReusableCell(CheckmarkCell.self, for: indexPath)
+            cell.bind(model: .init(title: localizedCellTitle(by: style), isChecked: itemModel.isChecked))
+            return cell
+        }
+    }
+
+    weak var delegate: ThemeSettingViewControllerDelegate?
+
+    lazy var rootView: UITableView = .init(frame: .zero, style: .insetGrouped).then {
+        $0.registerCell(CheckmarkCell.self)
+    }
+
+    override func loadView() {
+        self.view = rootView
+    }
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        self.view.backgroundColor = .systemGroupedBackground
+        self.navigationItem.title = WCString.theme
+
+        applyInitialSnapshotIfNoSections()
+    }
+
+    override func viewDidDisappear(_ animated: Bool) {
+        super.viewDidDisappear(animated)
+
+        if self.isMovingFromParent {
+            delegate?.viewControllerDidPop(self)
+        }
+    }
+
+    /// 현재 DataSource 에 적용된 Snapshot 이 없다면 초기 Snapshot 을 적용합니다.
+    /// - Returns: 현재 DataSource 에 적용된 Snapshot 이 있다면 해당 Snapshot 을 반환, 없다면 새로 적용한 Snapshot 을 반환합니다.
+    @discardableResult
+    func applyInitialSnapshotIfNoSections() -> NSDiffableDataSourceSnapshot<SectionIdentifier, ItemIdentifier> {
+        let currenetSnapshot = dataSource.snapshot()
+
+        if currenetSnapshot.sectionIdentifiers.isNotEmpty {
+            return currenetSnapshot
+        }
+
+        var snapshot: NSDiffableDataSourceSnapshot<SectionIdentifier, ItemIdentifier> = .init()
+        let itemIdentifiers = Array(itemModels.keys)
+
+        snapshot.appendSections([.theme])
+        snapshot.appendItems(itemIdentifiers, toSection: .theme)
+        dataSource.applySnapshotUsingReloadData(snapshot)
+        return snapshot
+    }
+
+    func bind(reactor: ThemeSettingReactor) {
+        // Action
+        self.rx.sentMessage(#selector(viewDidLoad))
+            .map { _ in Reactor.Action.viewDidLoad }
+            .bind(to: reactor.action)
+            .disposed(by: self.disposeBag)
+
+        rootView.rx.itemSelected
+            .doOnNext { [weak self] in self?.rootView.deselectRow(at: $0, animated: false) }
+            .compactMap { [weak self] indexPath in
+                guard case .theme(let style) = self?.dataSource.itemIdentifier(for: indexPath) else {
+                    assertionFailure("Selected invalid item.")
+                    return nil
+                }
+                return style
+            }
+            .map(Reactor.Action.selectStyle)
+            .bind(to: reactor.action)
+            .disposed(by: self.disposeBag)
+
+        // State
+        reactor.state
+            .map(\.selectedStyle)
+            .skip(1) // skip initialState
+            .asDriverOnErrorJustComplete()
+            .drive(with: self) { owner, selectedStyle in
+                var snapshot = owner.dataSource.snapshot()
+                snapshot = owner.applyInitialSnapshotIfNoSections()
+
+                owner.itemModels = owner.defaultItemModels
+                owner.itemModels[.theme(selectedStyle)] = .init(title: owner.localizedCellTitle(by: selectedStyle), isChecked: true)
+
+                snapshot.reconfigureItems(snapshot.itemIdentifiers(inSection: .theme))
+                owner.dataSource.apply(snapshot)
+            }
+            .disposed(by: self.disposeBag)
+    }
+
+    func localizedCellTitle(by style: UIUserInterfaceStyle) -> String {
+        switch style {
+        case .unspecified:
+            return WCString.system_mode
+        case .light:
+            return WCString.light_mode
+        case .dark:
+            return WCString.dark_mode
+        @unknown default:
+            assertionFailure("unkown cases.")
+            return ""
+        }
+    }
+
+}
diff --git a/Sources/iOSScenes/UserSettings/UserSettingsDataSource/UserSettingsItemModel.swift b/Sources/iOSScenes/UserSettings/UserSettingsDataSource/UserSettingsItemModel.swift
index 8c7ce7bf..cee35ab3 100644
--- a/Sources/iOSScenes/UserSettings/UserSettingsDataSource/UserSettingsItemModel.swift
+++ b/Sources/iOSScenes/UserSettings/UserSettingsDataSource/UserSettingsItemModel.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import Foundation
+import IOSSupport
 
 enum UserSettingsItemModel {
     case disclosureIndicator(DisclosureIndicatorCell.Model)
diff --git a/Sources/iOSScenes/UserSettings/UserSettingsReactor.swift b/Sources/iOSScenes/UserSettings/UserSettingsReactor.swift
index ca22cdc9..a65ee0eb 100644
--- a/Sources/iOSScenes/UserSettings/UserSettingsReactor.swift
+++ b/Sources/iOSScenes/UserSettings/UserSettingsReactor.swift
@@ -7,7 +7,7 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
 final class UserSettingsReactor: Reactor {
@@ -47,12 +47,12 @@ final class UserSettingsReactor: Reactor {
 
     let userSettingsUseCase: UserSettingsUseCaseProtocol
     let googleDriveUseCase: ExternalStoreUseCaseProtocol
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
 
     init(
         userSettingsUseCase: UserSettingsUseCaseProtocol,
         googleDriveUseCase: ExternalStoreUseCaseProtocol,
-        globalAction: GlobalReactorAction
+        globalAction: GlobalAction
     ) {
         self.userSettingsUseCase = userSettingsUseCase
         self.googleDriveUseCase = googleDriveUseCase
diff --git a/Sources/iOSScenes/UserSettings/UserSettingsViewController.swift b/Sources/iOSScenes/UserSettings/UserSettingsViewController.swift
index 274abdb8..f437f530 100644
--- a/Sources/iOSScenes/UserSettings/UserSettingsViewController.swift
+++ b/Sources/iOSScenes/UserSettings/UserSettingsViewController.swift
@@ -7,7 +7,7 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import RxSwift
 import RxUtility
@@ -110,10 +110,6 @@ final class UserSettingsViewController: RxBaseViewController, View, UserSettings
     }
 
     override func bindAction() {
-        guard let reactor = self.reactor else {
-            preconditionFailure("After initialization, reactor is not assigned.")
-        }
-
         let itemSelectedEvent = settingsTableView.rx.itemSelected.asSignal()
             .doOnNext { [weak self] in self?.settingsTableView.deselectRow(at: $0, animated: true) }
 
diff --git a/Sources/iOSScenes/WordAddition/WordAdditionViewController.swift b/Sources/iOSScenes/WordAddition/WordAdditionViewController.swift
index 0776ba52..35a665ac 100644
--- a/Sources/iOSScenes/WordAddition/WordAdditionViewController.swift
+++ b/Sources/iOSScenes/WordAddition/WordAdditionViewController.swift
@@ -5,7 +5,7 @@
 //  Created by Jaewon Yun on 2023/09/09.
 //
 
-import iOSSupport
+import IOSSupport
 import RxSwift
 import RxCocoa
 import RxUtility
@@ -13,10 +13,7 @@ import SnapKit
 import Then
 import UIKit
 
-public protocol WordAdditionViewControllerDelegate: AnyObject {
-
-    func didFinishInteration()
-
+public protocol WordAdditionViewControllerDelegate: AnyObject, ViewControllerDelegate {
 }
 
 public protocol WordAdditionViewControllerProtocol: UIViewController {
@@ -34,6 +31,13 @@ final class WordAdditionViewController: RxBaseViewController, WordAdditionViewCo
         $0.borderStyle = .roundedRect
     }
 
+    let duplicatedWordAlertLabel: UILabel = .init().then {
+        $0.text = WCString.duplicate_word
+        $0.textColor = .systemRed
+        $0.adjustsFontForContentSizeCategory = true
+        $0.font = .preferredFont(forTextStyle: .footnote)
+    }
+
     lazy var cancelBarButton: UIBarButtonItem = .init(systemItem: .cancel)
 
     lazy var doneBarButton: UIBarButtonItem = .init(systemItem: .done).then {
@@ -58,11 +62,17 @@ final class WordAdditionViewController: RxBaseViewController, WordAdditionViewCo
 
     func setupSubviews() {
         self.view.addSubview(wordTextField)
+        self.view.addSubview(duplicatedWordAlertLabel)
 
         wordTextField.snp.makeConstraints { make in
             make.top.equalTo(self.view.safeAreaLayoutGuide).offset(10)
             make.leading.trailing.equalTo(self.view.safeAreaLayoutGuide).inset(20)
         }
+
+        duplicatedWordAlertLabel.snp.makeConstraints { make in
+            make.leading.trailing.equalTo(self.view.safeAreaLayoutGuide).inset(22)
+            make.top.equalTo(wordTextField.snp.bottom).offset(10)
+        }
     }
 
     func setupNavigationBar() {
@@ -78,7 +88,7 @@ final class WordAdditionViewController: RxBaseViewController, WordAdditionViewCo
             return
         }
         let input: WordAdditionViewModel.Input = .init(
-            wordText: wordTextField.rx.text.orEmpty.asDriver(),
+            wordText: wordTextField.rx.text.orEmpty.asDriver().distinctUntilChanged(),
             saveAttempt: doneBarButton.rx.tap.asSignal(),
             dismissAttempt: Signal.merge(
                 cancelBarButton.rx.tap.asSignal(),
@@ -90,20 +100,27 @@ final class WordAdditionViewController: RxBaseViewController, WordAdditionViewCo
         [
             output.saveComplete
                 .emit(with: self, onNext: { owner, _ in
-                    owner.delegate?.didFinishInteration()
+                    owner.delegate?.viewControllerMustBeDismissed(owner)
                 }),
-            output.wordTextIsNotEmpty
-                .drive(doneBarButton.rx.isEnabled),
             output.reconfirmDismiss
                 .emit(with: self, onNext: { owner, _ in
                     owner.presentDismissActionSheet {
-                        owner.delegate?.didFinishInteration()
+                        owner.delegate?.viewControllerMustBeDismissed(owner)
                     }
                 }),
             output.dismissComplete
                 .emit(with: self, onNext: { owner, _ in
-                    owner.delegate?.didFinishInteration()
+                    owner.delegate?.viewControllerMustBeDismissed(owner)
                 }),
+            output.enteredWordIsDuplicated
+                .distinctUntilChanged()
+                .map { !$0 }
+                .drive(duplicatedWordAlertLabel.rx.isHidden),
+            Driver.zip([
+                output.wordTextIsNotEmpty,
+                output.enteredWordIsDuplicated,
+            ]).map { $0[0] && !$0[1] }
+                .drive(doneBarButton.rx.isEnabled),
         ]
             .forEach { $0.disposed(by: disposeBag) }
     }
diff --git a/Sources/iOSScenes/WordAddition/WordAdditionViewModel.swift b/Sources/iOSScenes/WordAddition/WordAdditionViewModel.swift
index 0f32cad4..24c6ce2f 100644
--- a/Sources/iOSScenes/WordAddition/WordAdditionViewModel.swift
+++ b/Sources/iOSScenes/WordAddition/WordAdditionViewModel.swift
@@ -7,8 +7,8 @@
 
 import Domain
 import Foundation
-import FoundationExtension
-import iOSSupport
+import FoundationPlus
+import IOSSupport
 import RxSwift
 import RxCocoa
 import RxUtility
@@ -22,7 +22,7 @@ final class WordAdditionViewModel: ViewModelType {
     }
 
     func transform(input: Input) -> Output {
-        let initialWordText = ""
+        let initialWordText = "" // 새 단어를 추가할때는 초기 단어가 없으므로
 
         let hasChanges = input.wordText.map { $0 != initialWordText }
 
@@ -36,7 +36,7 @@ final class WordAdditionViewModel: ViewModelType {
                     .asSignalOnErrorJustComplete()
             }
             .doOnNext { _ in
-                GlobalReactorAction.shared.didAddWord.accept(())
+                GlobalAction.shared.didAddWord.accept(())
             }
 
         let wordTextIsNotEmpty = input.wordText.map(\.isNotEmpty)
@@ -53,11 +53,18 @@ final class WordAdditionViewModel: ViewModelType {
             .mapToVoid()
             .asSignalOnErrorJustComplete()
 
+        let enteredWordIsDuplicated = input.wordText
+            .flatMapLatest { word in
+                return self.wordUseCase.isWordDuplicated(word)
+                    .asDriverOnErrorJustComplete()
+            }
+
         return .init(
             saveComplete: saveComplete,
             wordTextIsNotEmpty: wordTextIsNotEmpty,
             reconfirmDismiss: reconfirmDismiss,
-            dismissComplete: dismissComplete
+            dismissComplete: dismissComplete,
+            enteredWordIsDuplicated: enteredWordIsDuplicated
         )
     }
 
@@ -81,10 +88,13 @@ extension WordAdditionViewModel {
 
         let wordTextIsNotEmpty: Driver<Bool>
 
+        /// Dismiss 해야하는지 재확인이 필요할때 next 이벤트가 방출됩니다.
         let reconfirmDismiss: Signal<Void>
 
         let dismissComplete: Signal<Void>
 
+        /// 입력되어 있는 단어가 중복된 단어인지 여부
+        var enteredWordIsDuplicated: Driver<Bool>
     }
 
 }
diff --git a/Sources/iOSScenes/WordChecking/Subviews/WordChecking+ChangeWordButton.swift b/Sources/iOSScenes/WordChecking/Subviews/WordChecking+ChangeWordButton.swift
index eb4c190b..e0b71be6 100644
--- a/Sources/iOSScenes/WordChecking/Subviews/WordChecking+ChangeWordButton.swift
+++ b/Sources/iOSScenes/WordChecking/Subviews/WordChecking+ChangeWordButton.swift
@@ -5,7 +5,7 @@
 //  Created by Jaewon Yun on 2023/09/11.
 //
 
-import iOSSupport
+import IOSSupport
 import UIKit
 
 extension WordCheckingView {
diff --git a/Sources/iOSScenes/WordChecking/TranslationWeb/TranslationWebViewController.swift b/Sources/iOSScenes/WordChecking/TranslationWeb/TranslationWebViewController.swift
index df633280..293d3fc2 100644
--- a/Sources/iOSScenes/WordChecking/TranslationWeb/TranslationWebViewController.swift
+++ b/Sources/iOSScenes/WordChecking/TranslationWeb/TranslationWebViewController.swift
@@ -7,7 +7,7 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import Then
 import UIKit
 import WebKit
diff --git a/Sources/iOSScenes/WordChecking/WordCheckingReactor.swift b/Sources/iOSScenes/WordChecking/WordCheckingReactor.swift
index f5f55610..afa66106 100644
--- a/Sources/iOSScenes/WordChecking/WordCheckingReactor.swift
+++ b/Sources/iOSScenes/WordChecking/WordCheckingReactor.swift
@@ -8,9 +8,20 @@
 
 import Domain
 import Foundation
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
+enum WordCheckingReactorError: Error {
+
+    enum AddWordFailureReason {
+        case duplicatedWord(word: String)
+        case unknown(word: String)
+    }
+
+    case addWordFailed(reason: AddWordFailureReason)
+
+}
+
 final class WordCheckingReactor: Reactor {
 
     enum Action {
@@ -27,12 +38,14 @@ final class WordCheckingReactor: Reactor {
         case setCurrentWord(Word?)
         case setSourceLanguage(TranslationLanguage)
         case setTargetLanguage(TranslationLanguage)
+        case showAddCompleteToast(Result<String, WordCheckingReactorError>)
     }
 
     struct State {
         var currentWord: Word?
         var translationSourceLanguage: TranslationLanguage
         var translationTargetLanguage: TranslationLanguage
+        @Pulse var showAddCompleteToast: Result<String, WordCheckingReactorError>?
     }
 
     let initialState: State = State(
@@ -43,12 +56,12 @@ final class WordCheckingReactor: Reactor {
 
     let wordUseCase: WordUseCaseProtocol
     let userSettingsUseCase: UserSettingsUseCaseProtocol
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
 
     init(
         wordUseCase: WordUseCaseProtocol,
         userSettingsUseCase: UserSettingsUseCaseProtocol,
-        globalAction: GlobalReactorAction
+        globalAction: GlobalAction
     ) {
         self.wordUseCase = wordUseCase
         self.userSettingsUseCase = userSettingsUseCase
@@ -82,9 +95,23 @@ final class WordCheckingReactor: Reactor {
             let newWord: Word = .init(word: newWord)
             return wordUseCase.addNewWord(newWord)
                 .asObservable()
-                .flatMap { self.wordUseCase.getCurrentUnmemorizedWord() }
-                .map(Mutation.setCurrentWord)
-                .catchAndReturn(.setCurrentWord(nil))
+                .flatMap { _ in self.wordUseCase.getCurrentUnmemorizedWord() }
+                .flatMap { currentWord -> Observable<Mutation> in
+                    return .merge([
+                        .just(.setCurrentWord(currentWord)),
+                        .just(.showAddCompleteToast(.success(newWord.word))),
+                    ])
+                }
+                .catch { error in
+                    switch error {
+                    case WordUseCaseError.saveFailed(reason: .duplicatedWord):
+                        return .just(.showAddCompleteToast(.failure(.addWordFailed(reason: .duplicatedWord(word: newWord.word)))))
+                    case WordUseCaseError.noMemorizingWords:
+                        return .just(.setCurrentWord(nil))
+                    default:
+                        return .just(.showAddCompleteToast(.failure(.addWordFailed(reason: .unknown(word: newWord.word)))))
+                    }
+                }
 
         case .updateToNextWord:
             return wordUseCase.updateToNextWord()
@@ -164,6 +191,8 @@ final class WordCheckingReactor: Reactor {
             state.translationSourceLanguage = translationSourceLanguage
         case .setTargetLanguage(let translationTargetLanguage):
             state.translationTargetLanguage = translationTargetLanguage
+        case .showAddCompleteToast(let result):
+            state.showAddCompleteToast = result
         }
 
         return state
diff --git a/Sources/iOSScenes/WordChecking/WordCheckingView.swift b/Sources/iOSScenes/WordChecking/WordCheckingView.swift
index 5166ce0b..cfe85bc8 100644
--- a/Sources/iOSScenes/WordChecking/WordCheckingView.swift
+++ b/Sources/iOSScenes/WordChecking/WordCheckingView.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SnapKit
 import Then
 import UIKit
diff --git a/Sources/iOSScenes/WordChecking/WordCheckingViewController.swift b/Sources/iOSScenes/WordChecking/WordCheckingViewController.swift
index a2828ea0..b1052c75 100644
--- a/Sources/iOSScenes/WordChecking/WordCheckingViewController.swift
+++ b/Sources/iOSScenes/WordChecking/WordCheckingViewController.swift
@@ -5,7 +5,7 @@
 //  Created by Jaewon Yun on 2023/08/23.
 //
 
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import RxSwift
 import RxCocoa
@@ -169,6 +169,27 @@ final class WordCheckingViewController: RxBaseViewController, View, WordChecking
                 owner.setAccessibilityLanguage()
             }
             .disposed(by: self.disposeBag)
+
+        reactor.pulse(\.$showAddCompleteToast)
+            .asSignalOnErrorJustComplete()
+            .emit(with: self) { owner, showAddCompleteToast in
+                guard let showAddCompleteToast = showAddCompleteToast else { return }
+                switch showAddCompleteToast {
+                case .success(let word):
+                    owner.view.makeToast(WCString.word_added_successfully(word: word), duration: 2.0, position: .top)
+                case .failure(let error):
+                    switch error {
+                    case .addWordFailed(let reason):
+                        switch reason {
+                        case .duplicatedWord:
+                            owner.view.makeToast(WCString.already_added_word, duration: 2.0, position: .top)
+                        case .unknown(let word):
+                            owner.view.makeToast(WCString.word_added_failed(word: word), duration: 2.0, position: .top)
+                        }
+                    }
+                }
+            }
+            .disposed(by: self.disposeBag)
     }
 
     func setAccessibilityLanguage() {
@@ -188,15 +209,13 @@ final class WordCheckingViewController: RxBaseViewController, View, WordChecking
             }
             alertController.addAction(cancelAction)
 
-            let addAction: UIAlertAction = .init(title: WCString.add, style: .default) { [weak self] _ in
+            let addAction: UIAlertAction = .init(title: WCString.add, style: .default) { _ in
                 guard let word = alertController.textFields?.first?.text else {
                     assertionFailure("Failed to get word.")
                     return
                 }
 
                 observer(.success(word))
-
-                self?.view.makeToast(WCString.word_added_successfully(word: word), duration: 1.2, position: .top)
             }
             alertController.addAction(addAction)
 
diff --git a/Sources/iOSScenes/WordDetail/WordDetailReactor.swift b/Sources/iOSScenes/WordDetail/WordDetailReactor.swift
index 77d84d86..f387f2ef 100644
--- a/Sources/iOSScenes/WordDetail/WordDetailReactor.swift
+++ b/Sources/iOSScenes/WordDetail/WordDetailReactor.swift
@@ -8,7 +8,7 @@
 
 import Domain
 import Foundation
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
 final class WordDetailReactor: Reactor {
@@ -17,21 +17,45 @@ final class WordDetailReactor: Reactor {
         case viewDidLoad
         case beginEditing
         case doneEditing
-        case editWord(String)
+
+        /// 현재 입력된 단어
+        case enteredWord(String)
+
         case changeMemorizedState(MemorizedState)
     }
 
     enum Mutation {
         case updateWord(Word)
         case markAsEditing
+
+        /// 현재 입력된 단어를 중복된 단어로 표시할지 결정하는 Mutation
+        case setDuplicated(Bool)
+
+        /// 현재 입력된 단어의 비어있음 상태를 결정하는 Mutation
+        case setEmpty(Bool)
     }
 
     struct State {
+
+        /// 현재 입력된 단어
         var word: Word
+
+        /// 현재 화면에서 변경사항이 발생했는지 여부를 나타내는 값
         var hasChanges: Bool
+
+        /// 입력되어 있는 단어가 중복된 단어인지 여부를 나타내는 값
+        var enteredWordIsDuplicated: Bool
+
+        /// 현재 입력된 단어가 비어있는지 여부를 나타내는 값
+        var enteredWordIsEmpty: Bool
     }
 
-    var initialState: State = State(word: .empty, hasChanges: false)
+    var initialState: State = State(
+        word: .empty,
+        hasChanges: false,
+        enteredWordIsDuplicated: false,
+        enteredWordIsEmpty: false // Detail 화면에서는 항상 초기 단어가 있으므로
+    )
 
     /// 현재 보여지고 있는 단어의 UUID 입니다.
     let uuid: UUID
@@ -39,12 +63,12 @@ final class WordDetailReactor: Reactor {
     /// 편집되기 전 원래 단어입니다. viewDidLoad 가 호출될 때 초기화됩니다.
     private(set) var originWord: String?
 
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
     let wordUseCase: WordUseCaseProtocol
 
     init(
         uuid: UUID,
-        globalAction: GlobalReactorAction,
+        globalAction: GlobalAction,
         wordUseCase: WordUseCaseProtocol
     ) {
         self.uuid = uuid
@@ -73,10 +97,24 @@ final class WordDetailReactor: Reactor {
                 .asObservable()
                 .flatMap { _ -> Observable<Mutation> in return .empty() }
 
-        case .editWord(let word):
-            self.currentState.word.word = word
+        case .enteredWord(let enteredWord):
+            let setDuplicatedMutation = wordUseCase.isWordDuplicated(enteredWord)
+                .asObservable()
+                .map { [weak self] isWordDuplicated in
+                    if isWordDuplicated && (enteredWord != self?.originWord) { // 원래 단어와 달라야 중복이므로
+                        return Mutation.setDuplicated(true)
+                    } else {
+                        return Mutation.setDuplicated(false)
+                    }
+                }
+
+            self.currentState.word.word = enteredWord
 
-            return .just(.updateWord(self.currentState.word))
+            return .merge([
+                .just(.updateWord(self.currentState.word)),
+                setDuplicatedMutation,
+                .just(.setEmpty(enteredWord.isEmpty)),
+            ])
 
         case .changeMemorizedState(let state):
             self.currentState.word.memorizedState = state
@@ -96,6 +134,10 @@ final class WordDetailReactor: Reactor {
             state.word = word
         case .markAsEditing:
             state.hasChanges = true
+        case .setDuplicated(let enteredWordIsDuplicated):
+            state.enteredWordIsDuplicated = enteredWordIsDuplicated
+        case .setEmpty(let enteredWordIsEmpty):
+            state.enteredWordIsEmpty = enteredWordIsEmpty
         }
 
         return state
diff --git a/Sources/iOSScenes/WordDetail/WordDetailViewController.swift b/Sources/iOSScenes/WordDetail/WordDetailViewController.swift
index db0d8476..eedc68e9 100644
--- a/Sources/iOSScenes/WordDetail/WordDetailViewController.swift
+++ b/Sources/iOSScenes/WordDetail/WordDetailViewController.swift
@@ -6,17 +6,15 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import ReactorKit
+import RxCocoa
 import SnapKit
 import Then
 import UIKit
 import Utility
 
-public protocol WordDetailViewControllerDelegate: AnyObject {
-
-    func willFinishInteraction()
-
+public protocol WordDetailViewControllerDelegate: AnyObject, ViewControllerDelegate {
 }
 
 public protocol WordDetailViewControllerProtocol: UIViewController {
@@ -38,6 +36,13 @@ final class WordDetailViewController: RxBaseViewController, WordDetailViewContro
         $0.accessibilityIdentifier = AccessibilityIdentifier.WordDetail.wordTextField
     }
 
+    let duplicatedWordAlertLabel: UILabel = .init().then {
+        $0.text = WCString.duplicate_word
+        $0.textColor = .systemRed
+        $0.adjustsFontForContentSizeCategory = true
+        $0.font = .preferredFont(forTextStyle: .footnote)
+    }
+
     lazy var memorizationStatePopupButton: UIButton = {
         var config: UIButton.Configuration = .bordered()
         config.baseBackgroundColor = .systemGray5
@@ -80,6 +85,7 @@ final class WordDetailViewController: RxBaseViewController, WordDetailViewContro
 
     private func setupSubviews() {
         self.view.addSubview(wordTextField)
+        self.view.addSubview(duplicatedWordAlertLabel)
         self.view.addSubview(memorizationStatePopupButton)
 
         wordTextField.snp.makeConstraints { make in
@@ -87,8 +93,13 @@ final class WordDetailViewController: RxBaseViewController, WordDetailViewContro
             make.leading.trailing.equalTo(self.view.safeAreaLayoutGuide).inset(20)
         }
 
+        duplicatedWordAlertLabel.snp.makeConstraints { make in
+            make.leading.trailing.equalTo(self.view.safeAreaLayoutGuide).inset(22)
+            make.top.equalTo(wordTextField.snp.bottom).offset(10)
+        }
+
         memorizationStatePopupButton.snp.makeConstraints { make in
-            make.top.equalTo(wordTextField.snp.bottom).offset(20)
+            make.top.equalTo(duplicatedWordAlertLabel.snp.bottom).offset(20)
             make.leading.trailing.equalTo(self.view.safeAreaLayoutGuide).inset(20)
         }
     }
@@ -106,10 +117,10 @@ final class WordDetailViewController: RxBaseViewController, WordDetailViewContro
             .drive(with: self) { owner, _ in
                 if owner.reactor!.currentState.hasChanges {
                     owner.presentDismissActionSheet {
-                        owner.delegate?.willFinishInteraction()
+                        owner.delegate?.viewControllerMustBeDismissed(owner)
                     }
                 } else {
-                    owner.delegate?.willFinishInteraction()
+                    owner.delegate?.viewControllerMustBeDismissed(owner)
                 }
             }
             .disposed(by: self.disposeBag)
@@ -122,20 +133,26 @@ final class WordDetailViewController: RxBaseViewController, WordDetailViewContro
 extension WordDetailViewController: View {
 
     func bind(reactor: WordDetailReactor) {
-        // Action
+        // MARK: Action
+
         self.rx.sentMessage(#selector(self.viewDidLoad))
             .map { _ in Reactor.Action.viewDidLoad }
             .bind(to: reactor.action)
             .disposed(by: self.disposeBag)
 
         doneBarButton.rx.tap
-            .doOnNext { [weak self] _ in self?.delegate?.willFinishInteraction() }
+            .doOnNext { [weak self] _ in
+                guard let self = self else { return }
+                self.delegate?.viewControllerMustBeDismissed(self)
+            }
             .map { Reactor.Action.doneEditing }
             .bind(to: reactor.action)
             .disposed(by: self.disposeBag)
 
         wordTextField.rx.text.orEmpty
-            .map(Reactor.Action.editWord)
+            .skip(1) // 초깃값("") 무시
+            .distinctUntilChanged()
+            .map(Reactor.Action.enteredWord)
             .bind(to: reactor.action)
             .disposed(by: self.disposeBag)
 
@@ -146,7 +163,8 @@ extension WordDetailViewController: View {
             .bind(to: reactor.action)
             .disposed(by: self.disposeBag)
 
-        // State
+        // MARK: State
+
         reactor.state
             .map(\.hasChanges)
             .distinctUntilChanged()
@@ -175,6 +193,28 @@ extension WordDetailViewController: View {
                 }
             }
             .disposed(by: self.disposeBag)
+
+        // 완료 버튼 활성화/비활성화
+        Driver.zip([
+            reactor.state
+                .map(\.enteredWordIsEmpty)
+                .asDriverOnErrorJustComplete(),
+            reactor.state
+                .map(\.enteredWordIsDuplicated)
+                .asDriverOnErrorJustComplete(),
+        ]).map { !$0[0] && !$0[1] }
+            .drive(doneBarButton.rx.isEnabled)
+            .disposed(by: self.disposeBag)
+
+        // 중복 단어 경고 레이블 표시/비표시
+        reactor.state
+            .map(\.enteredWordIsDuplicated)
+            .distinctUntilChanged()
+            .asDriverOnErrorJustComplete()
+            .drive(with: self) { owner, enteredWordIsDuplicated in
+                owner.duplicatedWordAlertLabel.isHidden = !enteredWordIsDuplicated
+            }
+            .disposed(by: self.disposeBag)
     }
 
 }
@@ -185,12 +225,12 @@ extension WordDetailViewController: UIAdaptivePresentationControllerDelegate {
 
     func presentationControllerDidAttemptToDismiss(_ presentationController: UIPresentationController) {
         self.presentDismissActionSheet {
-            self.delegate?.willFinishInteraction()
+            self.delegate?.viewControllerMustBeDismissed(self)
         }
     }
 
-    func presentationControllerWillDismiss(_ presentationController: UIPresentationController) {
-        delegate?.willFinishInteraction()
+    func presentationControllerDidDismiss(_ presentationController: UIPresentationController) {
+        delegate?.viewControllerDidDismiss(self)
     }
 
 }
diff --git a/Sources/iOSScenes/WordList/WordListReactor.swift b/Sources/iOSScenes/WordList/WordListReactor.swift
index df8245aa..6d0a83e9 100644
--- a/Sources/iOSScenes/WordList/WordListReactor.swift
+++ b/Sources/iOSScenes/WordList/WordListReactor.swift
@@ -8,7 +8,7 @@
 
 import Domain
 import Foundation
-import iOSSupport
+import IOSSupport
 import ReactorKit
 
 final class WordListReactor: Reactor {
@@ -33,10 +33,10 @@ final class WordListReactor: Reactor {
 
     var initialState: State = State(listType: .all, wordList: [])
 
-    let globalAction: GlobalReactorAction
+    let globalAction: GlobalAction
     let wordUseCase: WordUseCaseProtocol
 
-    init(globalAction: GlobalReactorAction, wordUseCase: WordUseCaseProtocol) {
+    init(globalAction: GlobalAction, wordUseCase: WordUseCaseProtocol) {
         self.globalAction = globalAction
         self.wordUseCase = wordUseCase
     }
diff --git a/Sources/iOSScenes/WordList/WordListViewController.swift b/Sources/iOSScenes/WordList/WordListViewController.swift
index 43cc629f..90306825 100644
--- a/Sources/iOSScenes/WordList/WordListViewController.swift
+++ b/Sources/iOSScenes/WordList/WordListViewController.swift
@@ -5,7 +5,7 @@
 //  Created by Jaewon Yun on 2023/08/25.
 //
 
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import RxUtility
 import SFSafeSymbols
diff --git a/Sources/iOSScenes/WordList/WordSearchResultsController.swift b/Sources/iOSScenes/WordList/WordSearchResultsController.swift
index 2e59d6b3..23f776dc 100644
--- a/Sources/iOSScenes/WordList/WordSearchResultsController.swift
+++ b/Sources/iOSScenes/WordList/WordSearchResultsController.swift
@@ -6,11 +6,10 @@
 //
 
 import Domain
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import SwinjectExtension
 import UIKit
-import WordDetail
 
 public protocol WordSearchResultsControllerDelegate: AnyObject {
 
@@ -152,13 +151,3 @@ extension WordSearchResultsController: UISearchResultsUpdating {
     }
 
 }
-
-// MARK: - WordDetailViewControllerDelegate
-
-extension WordSearchResultsController: WordDetailViewControllerDelegate {
-
-    func willFinishInteraction() {
-        self.presentingViewController?.tabBarController?.dismiss(animated: true)
-    }
-
-}
diff --git a/Sources/iOSSupport/Common/Domain.ThemeStyle+mapping.swift b/Sources/iOSSupport/Common/Domain.ThemeStyle+mapping.swift
new file mode 100644
index 00000000..8e0b0649
--- /dev/null
+++ b/Sources/iOSSupport/Common/Domain.ThemeStyle+mapping.swift
@@ -0,0 +1,43 @@
+//
+//  Domain.ThemeStyle+mapping.swift
+//  iOSSupport
+//
+//  Created by Jaewon Yun on 2/7/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import Domain
+import UIKit
+
+extension Domain.ThemeStyle {
+
+    public func toUIKit() -> UIUserInterfaceStyle {
+        switch self {
+        case .system:
+            return .unspecified
+        case .light:
+            return .light
+        case .dark:
+            return .dark
+        }
+    }
+
+}
+
+extension UIUserInterfaceStyle {
+
+    public func toDomain() -> Domain.ThemeStyle {
+        switch self {
+        case .unspecified:
+            return .system
+        case .light:
+            return .light
+        case .dark:
+            return .dark
+        @unknown default:
+            assertionFailure("unkown cases.")
+            return .system
+        }
+    }
+
+}
diff --git a/Sources/iOSSupport/Common/GlobalReactorAction.swift b/Sources/iOSSupport/Common/GlobalAction.swift
similarity index 88%
rename from Sources/iOSSupport/Common/GlobalReactorAction.swift
rename to Sources/iOSSupport/Common/GlobalAction.swift
index 7573acd0..8c788be6 100644
--- a/Sources/iOSSupport/Common/GlobalReactorAction.swift
+++ b/Sources/iOSSupport/Common/GlobalAction.swift
@@ -11,9 +11,9 @@ import Foundation
 import RxSwift
 import RxCocoa
 
-public final class GlobalReactorAction {
+public final class GlobalAction {
 
-    public static let shared: GlobalReactorAction = .init()
+    public static let shared: GlobalAction = .init()
 
     private init() {}
 
diff --git a/Sources/iOSSupport/Common/GlobalState.swift b/Sources/iOSSupport/Common/GlobalState.swift
index d355de0a..e4f51054 100644
--- a/Sources/iOSSupport/Common/GlobalState.swift
+++ b/Sources/iOSSupport/Common/GlobalState.swift
@@ -6,22 +6,35 @@
 //  Copyright © 2024 woin2ee. All rights reserved.
 //
 
-import Foundation
+import UIKit
+import RxSwift
+import RxRelay
 
 /// 앱의 전역 상태를 가지는 객체입니다.
 ///
-/// - Warning: 앱의 전역 상태를 나타내므로 반드시 Singleton 으로 사용해야 합니다.
+/// 전역 상태를 초기화하기 위해 `initialize()` 인스턴스 함수를 호출하는것이 권장됩니다.
+///
+/// - Note: 앱의 전역 상태를 나타내므로 공유 객체로 정의되어 있습니다.
 public final class GlobalState {
 
     public static let shared: GlobalState = .init()
 
-    private init() {}
+    /// 고정된 상태 값으로 객체를 초기화합니다.
+    private init() {
+        self.hapticsIsOn = true
+        self.themeStyle = .init(value: .unspecified)
+    }
+
+    public var hapticsIsOn: Bool
 
-    public var hapticsIsOn: Bool!
+    public var themeStyle: BehaviorRelay<UIUserInterfaceStyle>
 
-    /// 전역 상태를 초기화 합니다.
-    public func initialize(hapticsIsOn: Bool) {
+    /// 전역 상태를 초기화합니다.
+    ///
+    /// 전달된 파라미터를 이용하여 전역 상태를 초기화합니다. 이 함수를 호출하여 초기화하지 않으면, 내부 생성자에서 고정된 값으로 전역 상태가 초기화됩니다.
+    public func initialize(hapticsIsOn: Bool, themeStyle: UIUserInterfaceStyle) {
         self.hapticsIsOn = hapticsIsOn
+        self.themeStyle = .init(value: themeStyle)
     }
 
 }
diff --git a/Sources/iOSSupport/Foundations/ViewControllerDelegate.swift b/Sources/iOSSupport/Foundations/ViewControllerDelegate.swift
new file mode 100644
index 00000000..0c6d7805
--- /dev/null
+++ b/Sources/iOSSupport/Foundations/ViewControllerDelegate.swift
@@ -0,0 +1,25 @@
+//
+//  ViewControllerDelegate.swift
+//  iPhoneDriver
+//
+//  Created by Jaewon Yun on 2/7/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import UIKit
+
+/// `UIViewController` 를 위한 기본적인 Delegate methods 가 정의되어 있는 Protocol 입니다.
+public protocol ViewControllerDelegate {
+
+    /// ViewController 가 Pop 되었음을 Delegate 에게 알립니다.
+    func viewControllerDidPop(_ viewController: UIViewController)
+
+    /// ViewController 가 Dismiss 되어야 함을 Delegate 에게 알립니다.
+    ///
+    /// 이 Delegate method 를 구현하는 Subclass 는 직접 ViewController 에 대한 Dismiss 처리를 해야합니다.
+    func viewControllerMustBeDismissed(_ viewController: UIViewController)
+
+    /// ViewController 가 Dismiss 되었음을 Delegate 에게 알립니다.
+    func viewControllerDidDismiss(_ viewController: UIViewController)
+
+}
diff --git a/Sources/iOSSupport/Localization/WCString.swift b/Sources/iOSSupport/Localization/WCString.swift
index 02b91c99..6c6efab1 100644
--- a/Sources/iOSSupport/Localization/WCString.swift
+++ b/Sources/iOSSupport/Localization/WCString.swift
@@ -63,6 +63,11 @@ public struct WCString {
         let localizedString = NSLocalizedString("%@_added_successfully", bundle: Bundle.module, comment: "단어 추가 완료 후 표시되는 메세지")
         return .init(format: localizedString, arguments: [word])
     }
+    public static let already_added_word = NSLocalizedString("already_added_word", bundle: Bundle.module, comment: "")
+    public static func word_added_failed(word: String) -> String {
+        let localizedString = NSLocalizedString("%@_added_failed", bundle: Bundle.module, comment: "알 수 없는 이유로 단어 추가 실패 후 표시되는 메세지")
+        return .init(format: localizedString, arguments: [word])
+    }
 
     public static let please_check_your_network_connection = NSLocalizedString("please_check_your_network_connection", bundle: Bundle.module, comment: "")
 
@@ -77,9 +82,15 @@ public struct WCString {
     public static let hapticsSettingsFooterTextWhenHapticsIsOn = NSLocalizedString("hapticsSettingsFooterTextWhenHapticsIsOn", bundle: Bundle.module, comment: "")
     public static let hapticsSettingsFooterTextWhenHapticsIsOff = NSLocalizedString("hapticsSettingsFooterTextWhenHapticsIsOff", bundle: Bundle.module, comment: "")
 
+    public static let theme = NSLocalizedString("theme", bundle: Bundle.module, comment: "")
+    public static let system_mode = NSLocalizedString("system_mode", bundle: Bundle.module, comment: "")
+    public static let light_mode = NSLocalizedString("light_mode", bundle: Bundle.module, comment: "")
+    public static let dark_mode = NSLocalizedString("dark_mode", bundle: Bundle.module, comment: "")
+
     public static let more_menu = NSLocalizedString("more_menu", bundle: Bundle.module, comment: "")
     public static let memorize_words = NSLocalizedString("memorize_words", bundle: Bundle.module, comment: "")
     public static let previous_word = NSLocalizedString("previous_word", bundle: Bundle.module, comment: "")
     public static let next_word = NSLocalizedString("next_word", bundle: Bundle.module, comment: "")
 
+    public static let duplicate_word = NSLocalizedString("duplicate_word", bundle: Bundle.module, comment: "")
 }
diff --git a/Sources/iOSScenes/UserSettings/Cells/ButtonCell.swift b/Sources/iOSSupport/UIKitExtension/Cells/ButtonCell.swift
similarity index 75%
rename from Sources/iOSScenes/UserSettings/Cells/ButtonCell.swift
rename to Sources/iOSSupport/UIKitExtension/Cells/ButtonCell.swift
index 60536acf..5cfb0be2 100644
--- a/Sources/iOSScenes/UserSettings/Cells/ButtonCell.swift
+++ b/Sources/iOSSupport/UIKitExtension/Cells/ButtonCell.swift
@@ -6,17 +6,21 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
 import UIKit
 
 /// 버튼 역할을 하기 위한 Cell 클래스 입니다.
 ///
 /// 버튼 가이드라인에 따른 텍스트 색상을 사용하세요.
-final class ButtonCell: UITableViewCell, ReusableIdentifying {
+public final class ButtonCell: UITableViewCell, ReusableIdentifying {
 
-    struct Model {
+    public struct Model {
         let title: String
         let textColor: UIColor
+
+        public init(title: String, textColor: UIColor) {
+            self.title = title
+            self.textColor = textColor
+        }
     }
 
     override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
@@ -29,7 +33,7 @@ final class ButtonCell: UITableViewCell, ReusableIdentifying {
         fatalError("init(coder:) has not been implemented")
     }
 
-    func bind(model: Model) {
+    public func bind(model: Model) {
         var config: UIListContentConfiguration = .cell()
         config.text = model.title
         config.textProperties.color = model.textColor
diff --git a/Sources/iOSScenes/UserSettings/Cells/DisclosureIndicatorCell.swift b/Sources/iOSSupport/UIKitExtension/Cells/DisclosureIndicatorCell.swift
similarity index 72%
rename from Sources/iOSScenes/UserSettings/Cells/DisclosureIndicatorCell.swift
rename to Sources/iOSSupport/UIKitExtension/Cells/DisclosureIndicatorCell.swift
index 5054dd46..fd1717c9 100644
--- a/Sources/iOSScenes/UserSettings/Cells/DisclosureIndicatorCell.swift
+++ b/Sources/iOSSupport/UIKitExtension/Cells/DisclosureIndicatorCell.swift
@@ -6,14 +6,18 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
 import UIKit
 
-final class DisclosureIndicatorCell: UITableViewCell, ReusableIdentifying {
+public final class DisclosureIndicatorCell: UITableViewCell, ReusableIdentifying {
 
-    struct Model {
+    public struct Model {
         let title: String
         let value: String?
+
+        public init(title: String, value: String? = nil) {
+            self.title = title
+            self.value = value
+        }
     }
 
     override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
@@ -26,7 +30,7 @@ final class DisclosureIndicatorCell: UITableViewCell, ReusableIdentifying {
         fatalError("init(coder:) has not been implemented")
     }
 
-    func bind(model: Model) {
+    public func bind(model: Model) {
         var config: UIListContentConfiguration = .valueCell()
         config.text = model.title
         config.secondaryText = model.value
diff --git a/Sources/iPhoneDriver/Coordinators/AppCoordinator.swift b/Sources/iPhoneDriver/Coordinators/AppCoordinator.swift
index 17fb93c2..51ce5516 100644
--- a/Sources/iPhoneDriver/Coordinators/AppCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/AppCoordinator.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SFSafeSymbols
 import Then
 import UIKit
diff --git a/Sources/iPhoneDriver/Coordinators/BasicCoordinator.swift b/Sources/iPhoneDriver/Coordinators/BasicCoordinator.swift
new file mode 100644
index 00000000..1205b477
--- /dev/null
+++ b/Sources/iPhoneDriver/Coordinators/BasicCoordinator.swift
@@ -0,0 +1,56 @@
+//
+//  BasicCoordinator.swift
+//  iPhoneDriver
+//
+//  Created by Jaewon Yun on 2/7/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+import IOSSupport
+import UIKit
+import Utility
+
+/// iOS 환경에서 동작하는 Coordinator 를 위한 Parent coordinator 클래스
+///
+/// - warning: Do not use instance of this class directly. Some methods in this class cause of fatal error.
+class BasicCoordinator: Coordinator {
+
+    weak var parentCoordinator: IOSSupport.Coordinator?
+    var childCoordinators: [IOSSupport.Coordinator] = []
+
+    let navigationController: UINavigationController
+
+    init(navigationController: UINavigationController) {
+        self.navigationController = navigationController
+    }
+
+    func start() {
+        abstractMethod()
+    }
+
+    func start<Arg1>(with argument: Arg1) {
+        abstractMethod()
+    }
+
+    func start<Arg1, Arg2>(with arguments: Arg1, _ arg2: Arg2) {
+        abstractMethod()
+    }
+
+}
+
+extension BasicCoordinator: ViewControllerDelegate {
+
+    func viewControllerDidPop(_ viewController: UIViewController) {
+        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
+    }
+
+    func viewControllerMustBeDismissed(_ viewController: UIViewController) {
+        navigationController.dismiss(animated: true) // In this case, `navigationController` property is represented the presented view controller.
+        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
+    }
+
+    func viewControllerDidDismiss(_ viewController: UIViewController) {
+        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
+    }
+
+}
diff --git a/Sources/iPhoneDriver/Coordinators/GeneralSettingsCoordinator.swift b/Sources/iPhoneDriver/Coordinators/GeneralSettingsCoordinator.swift
index abaedfd3..10abc12d 100644
--- a/Sources/iPhoneDriver/Coordinators/GeneralSettingsCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/GeneralSettingsCoordinator.swift
@@ -7,22 +7,13 @@
 //
 
 import GeneralSettings
-import iOSSupport
+import IOSSupport
 import UIKit
 import SwinjectDIContainer
 
-final class GeneralSettingsCoordinator: Coordinator {
+final class GeneralSettingsCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: iOSSupport.Coordinator?
-    var childCoordinators: [iOSSupport.Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: GeneralSettingsViewControllerProtocol = DIContainer.shared.resolver.resolve()
         viewController.delegate = self
         navigationController.pushViewController(viewController, animated: true)
@@ -32,9 +23,11 @@ final class GeneralSettingsCoordinator: Coordinator {
 
 extension GeneralSettingsCoordinator: GeneralSettingsViewControllerDelegate {
 
-    func willPopView() {
-        navigationController.popViewController(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
+    func didTapThemeSetting() {
+        let coordinator: ThemeSettingCoordinator = .init(navigationController: navigationController)
+        coordinator.parentCoordinator = self
+        self.childCoordinators.append(coordinator)
+        coordinator.start()
     }
 
 }
diff --git a/Sources/iPhoneDriver/Coordinators/LanguageSettingCoordinator.swift b/Sources/iPhoneDriver/Coordinators/LanguageSettingCoordinator.swift
index a1cded96..48fe5741 100644
--- a/Sources/iPhoneDriver/Coordinators/LanguageSettingCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/LanguageSettingCoordinator.swift
@@ -6,24 +6,15 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import LanguageSetting
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 
-final class LanguageSettingCoordinator: Coordinator {
+final class LanguageSettingCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start<Arg1>(with argument: Arg1) {
+    override func start<Arg1>(with argument: Arg1) {
         let viewController: LanguageSettingViewControllerProtocol = DIContainer.shared.resolver.resolve(argument: argument)
         viewController.delegate = self
         navigationController.pushViewController(viewController, animated: true)
@@ -32,10 +23,4 @@ final class LanguageSettingCoordinator: Coordinator {
 }
 
 extension LanguageSettingCoordinator: LanguageSettingViewControllerDelegate {
-
-    func viewMustPop() {
-        navigationController.popViewController(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
-    }
-
 }
diff --git a/Sources/iPhoneDriver/Coordinators/PushNotificationSettingsCoordinator.swift b/Sources/iPhoneDriver/Coordinators/PushNotificationSettingsCoordinator.swift
index 32f966d6..0595fe93 100644
--- a/Sources/iPhoneDriver/Coordinators/PushNotificationSettingsCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/PushNotificationSettingsCoordinator.swift
@@ -6,36 +6,20 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
 import PushNotificationSettings
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 
-final class PushNotificationSettingsCoordinator: Coordinator {
+final class PushNotificationSettingsCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: PushNotificationSettingsViewControllerProtocol = DIContainer.shared.resolver.resolve()
         viewController.delegate = self
-        navigationController.pushViewController(viewController, animated: true)
+        self.navigationController.pushViewController(viewController, animated: true)
     }
 
 }
 
 extension PushNotificationSettingsCoordinator: PushNotificationSettingsDelegate {
-
-    func willPopView() {
-        navigationController.popViewController(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
-    }
-
 }
diff --git a/Sources/iPhoneDriver/Coordinators/ThemeSettingCoordinator.swift b/Sources/iPhoneDriver/Coordinators/ThemeSettingCoordinator.swift
new file mode 100644
index 00000000..d23377d4
--- /dev/null
+++ b/Sources/iPhoneDriver/Coordinators/ThemeSettingCoordinator.swift
@@ -0,0 +1,18 @@
+import IOSSupport
+import SwinjectDIContainer
+import SwinjectExtension
+import UIKit
+import ThemeSetting
+
+final class ThemeSettingCoordinator: BasicCoordinator {
+
+    override func start() {
+        let viewController: ThemeSettingViewControllerProtocol = DIContainer.shared.resolver.resolve()
+        viewController.delegate = self
+        navigationController.pushViewController(viewController, animated: true)
+    }
+
+}
+
+extension ThemeSettingCoordinator: ThemeSettingViewControllerDelegate {
+}
diff --git a/Sources/iPhoneDriver/Coordinators/UserSettingsCoordinator.swift b/Sources/iPhoneDriver/Coordinators/UserSettingsCoordinator.swift
index 5a51a2d4..12edd6d8 100644
--- a/Sources/iPhoneDriver/Coordinators/UserSettingsCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/UserSettingsCoordinator.swift
@@ -6,26 +6,16 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import Domain
-import iOSSupport
+import IOSSupport
 import LanguageSetting
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 import UserSettings
 
-final class UserSettingsCoordinator: Coordinator {
+final class UserSettingsCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: UserSettingsViewControllerProtocol = DIContainer.shared.resolver.resolve()
         viewController.delegate = self
         navigationController.setViewControllers([viewController], animated: false)
diff --git a/Sources/iPhoneDriver/Coordinators/WordAdditionCoordinator.swift b/Sources/iPhoneDriver/Coordinators/WordAdditionCoordinator.swift
index b74b6472..ee4f613d 100644
--- a/Sources/iPhoneDriver/Coordinators/WordAdditionCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/WordAdditionCoordinator.swift
@@ -6,24 +6,15 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 import WordAddition
 
-final class WordAdditionCoordinator: Coordinator {
+final class WordAdditionCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: WordAdditionViewControllerProtocol = DIContainer.shared.resolver.resolve()
         viewController.delegate = self
         navigationController.setViewControllers([viewController], animated: true)
@@ -32,10 +23,4 @@ final class WordAdditionCoordinator: Coordinator {
 }
 
 extension WordAdditionCoordinator: WordAdditionViewControllerDelegate {
-
-    func didFinishInteration() {
-        navigationController.dismiss(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
-    }
-
 }
diff --git a/Sources/iPhoneDriver/Coordinators/WordCheckingCoordinator.swift b/Sources/iPhoneDriver/Coordinators/WordCheckingCoordinator.swift
index cc5e7ab1..3138bfb0 100644
--- a/Sources/iPhoneDriver/Coordinators/WordCheckingCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/WordCheckingCoordinator.swift
@@ -6,24 +6,15 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 import WordChecking
 
-final class WordCheckingCoordinator: Coordinator {
+final class WordCheckingCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: WordCheckingViewControllerProtocol = DIContainer.shared.resolver.resolve()
         navigationController.setViewControllers([viewController], animated: false)
     }
diff --git a/Sources/iPhoneDriver/Coordinators/WordDetailCoordinator.swift b/Sources/iPhoneDriver/Coordinators/WordDetailCoordinator.swift
index f815c34c..48c81afa 100644
--- a/Sources/iPhoneDriver/Coordinators/WordDetailCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/WordDetailCoordinator.swift
@@ -6,24 +6,15 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 import WordDetail
 
-final class WordDetailCoordinator: Coordinator {
+final class WordDetailCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start<Arg1>(with argument: Arg1) {
+    override func start<Arg1>(with argument: Arg1) {
         let viewController: WordDetailViewControllerProtocol = DIContainer.shared.resolver.resolve(argument: argument)
         viewController.delegate = self
         navigationController.setViewControllers([viewController], animated: false)
@@ -32,10 +23,4 @@ final class WordDetailCoordinator: Coordinator {
 }
 
 extension WordDetailCoordinator: WordDetailViewControllerDelegate {
-
-    func willFinishInteraction() {
-        navigationController.dismiss(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
-    }
-
 }
diff --git a/Sources/iPhoneDriver/Coordinators/WordListCoordinator.swift b/Sources/iPhoneDriver/Coordinators/WordListCoordinator.swift
index 44427ece..8f4a7f04 100644
--- a/Sources/iPhoneDriver/Coordinators/WordListCoordinator.swift
+++ b/Sources/iPhoneDriver/Coordinators/WordListCoordinator.swift
@@ -6,24 +6,15 @@
 //  Copyright © 2023 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SwinjectDIContainer
 import SwinjectExtension
 import UIKit
 import WordList
 
-final class WordListCoordinator: Coordinator {
+final class WordListCoordinator: BasicCoordinator {
 
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
+    override func start() {
         let viewController: WordListViewControllerProtocol = DIContainer.shared.resolver.resolve()
         viewController.delegate = self
         navigationController.setViewControllers([viewController], animated: false)
diff --git a/Sources/iPhoneDriver/RootTabBarController.swift b/Sources/iPhoneDriver/RootTabBarController.swift
index d3ec8f56..68fbba18 100644
--- a/Sources/iPhoneDriver/RootTabBarController.swift
+++ b/Sources/iPhoneDriver/RootTabBarController.swift
@@ -6,7 +6,7 @@
 //  Copyright © 2024 woin2ee. All rights reserved.
 //
 
-import iOSSupport
+import IOSSupport
 import SFSafeSymbols
 import Then
 import UIKit
diff --git a/Sources/iPhoneDriver/SceneDelegate.swift b/Sources/iPhoneDriver/SceneDelegate.swift
index 2bc6638f..978ceaf2 100644
--- a/Sources/iPhoneDriver/SceneDelegate.swift
+++ b/Sources/iPhoneDriver/SceneDelegate.swift
@@ -5,27 +5,29 @@
 //  Created by Jaewon Yun on 2023/08/23.
 //
 
-import iOSSupport
+import IOSSupport
+import RxSwift
 import UIKit
 
 class SceneDelegate: UIResponder, UIWindowSceneDelegate {
 
+    let disposeBag: DisposeBag = .init()
+
     var window: UIWindow?
 
     var appCoordinator: AppCoordinator?
 
-    let globalAction: GlobalReactorAction = .shared
+    let globalAction: GlobalAction = .shared
+    let globalState: GlobalState = .shared
 
     func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
         guard let windowScene = (scene as? UIWindowScene) else { return }
         window = .init(windowScene: windowScene)
         window?.makeKeyAndVisible()
 
-        let rootTabBarController: RootTabBarController = .shared
-        window?.rootViewController = rootTabBarController
+        setRootViewController()
 
-        appCoordinator = .init(rootTabBarController: rootTabBarController)
-        appCoordinator?.start()
+        subscribeGlobalAction()
     }
 
     func sceneWillEnterForeground(_ scene: UIScene) {
@@ -36,4 +38,21 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         globalAction.sceneDidBecomeActive.accept(())
     }
 
+    func setRootViewController() {
+        let rootTabBarController: RootTabBarController = .shared
+        window?.rootViewController = rootTabBarController
+
+        appCoordinator = .init(rootTabBarController: rootTabBarController)
+        appCoordinator?.start()
+    }
+
+    func subscribeGlobalAction() {
+        globalState.themeStyle
+            .asDriver()
+            .drive(with: self) { owner, userInterfaceStyle in
+                owner.window?.overrideUserInterfaceStyle = userInterfaceStyle
+            }
+            .disposed(by: disposeBag)
+    }
+
 }
diff --git a/TestPlans/FoundationExtension.xctestplan b/TestPlans/FoundationExtension.xctestplan
deleted file mode 100644
index 6c803c28..00000000
--- a/TestPlans/FoundationExtension.xctestplan
+++ /dev/null
@@ -1,24 +0,0 @@
-{
-  "configurations" : [
-    {
-      "id" : "8F663F64-D2ED-466D-B509-5E41EF98731F",
-      "name" : "Configuration 1",
-      "options" : {
-
-      }
-    }
-  ],
-  "defaultOptions" : {
-    "testTimeoutsEnabled" : true
-  },
-  "testTargets" : [
-    {
-      "target" : {
-        "containerPath" : "container:WordChecker.xcodeproj",
-        "identifier" : "0D0A048C4E8A1F30CBB8F2BE",
-        "name" : "FoundationExtensionTests"
-      }
-    }
-  ],
-  "version" : 1
-}
diff --git a/TestPlans/IntergrationTests.xctestplan b/TestPlans/IntergrationTests.xctestplan
index 17d9cfe5..c04a423c 100644
--- a/TestPlans/IntergrationTests.xctestplan
+++ b/TestPlans/IntergrationTests.xctestplan
@@ -148,13 +148,6 @@
         "name" : "WordListTests"
       }
     },
-    {
-      "target" : {
-        "containerPath" : "container:WordChecker.xcodeproj",
-        "identifier" : "0D0A048C4E8A1F30CBB8F2BE",
-        "name" : "FoundationExtensionTests"
-      }
-    },
     {
       "target" : {
         "containerPath" : "container:WordChecker.xcodeproj",
@@ -175,6 +168,13 @@
         "identifier" : "7C78BC2C06BF23C70DEE14AE",
         "name" : "InfrastructureTests"
       }
+    },
+    {
+      "target" : {
+        "containerPath" : "container:WordChecker.xcodeproj",
+        "identifier" : "E5AF7A03E6E737AD9E4136ED",
+        "name" : "ThemeSettingTests"
+      }
     }
   ],
   "version" : 1
diff --git a/TestPlans/ThemeSetting.xctestplan b/TestPlans/ThemeSetting.xctestplan
new file mode 100644
index 00000000..bff262de
--- /dev/null
+++ b/TestPlans/ThemeSetting.xctestplan
@@ -0,0 +1,12 @@
+{
+  "configurations" : [
+
+  ],
+  "defaultOptions" : {
+    "testTimeoutsEnabled" : true
+  },
+  "testTargets" : [
+
+  ],
+  "version" : 1
+}
diff --git a/Tests/DomainTests/WordUseCaseTests.swift b/Tests/DomainTests/WordUseCaseTests.swift
index 13cf1dbe..809be3bd 100644
--- a/Tests/DomainTests/WordUseCaseTests.swift
+++ b/Tests/DomainTests/WordUseCaseTests.swift
@@ -198,6 +198,50 @@ final class WordUseCaseTests: XCTestCase {
         XCTAssertNotEqual(try sut.getCurrentUnmemorizedWord().toBlocking().single(), oldCurrentWord)
     }
 
+    func test_addDuplicatedWord() throws {
+        // Given
+        let duplicatedWord = unmemorizedWordList[0]
+
+        // When
+        let addNewWord = sut.addNewWord(duplicatedWord)
+            .toBlocking()
+
+        // Then
+        XCTAssertThrowsError(try addNewWord.single()) { error in
+            switch error {
+            case WordUseCaseError.saveFailed(reason: .duplicatedWord):
+                break
+            default:
+                XCTFail()
+            }
+        }
+    }
+
+    func test_isWordDuplicated() throws {
+        // Given
+        let duplicatedWord = unmemorizedWordList[0]
+
+        // When
+        let isWordDuplicated = try sut.isWordDuplicated(duplicatedWord.word)
+            .toBlocking()
+            .single()
+
+        // Then
+        XCTAssertTrue(isWordDuplicated)
+    }
+
+    func test_throwError_whenUpdateToDuplicatedWord() {
+        // Given
+        let duplicatedWord: Word = .init(uuid: unmemorizedWordList[0].uuid, word: "J") // 단어 A 를 J(중복) 로 업데이트
+
+        // When
+        let updateWord = sut.updateWord(by: duplicatedWord.uuid, to: duplicatedWord)
+            .toBlocking()
+
+        // Then
+        XCTAssertThrowsError(try updateWord.single())
+    }
+
 }
 
 // MARK: - Helpers
diff --git a/Tests/FoundationExtensionTests/FoundationExtensionTests.swift b/Tests/FoundationExtensionTests/FoundationExtensionTests.swift
deleted file mode 100644
index 7fce248d..00000000
--- a/Tests/FoundationExtensionTests/FoundationExtensionTests.swift
+++ /dev/null
@@ -1,18 +0,0 @@
-@testable import FoundationExtension
-
-import XCTest
-
-final class FoundationExtensionTests: XCTestCase {
-
-    func test_isNotEmpty() {
-        // Given
-        let string: String = ""
-
-        // When
-        let isNotEmpty = string.isNotEmpty
-
-        // Then
-        XCTAssertEqual(isNotEmpty, false)
-    }
-
-}
diff --git a/Tests/InfrastructureTests/UserDefaults/UserSettingsRepositoryTests.swift b/Tests/InfrastructureTests/UserDefaults/UserSettingsRepositoryTests.swift
index f1402b6d..49d551f8 100644
--- a/Tests/InfrastructureTests/UserDefaults/UserSettingsRepositoryTests.swift
+++ b/Tests/InfrastructureTests/UserDefaults/UserSettingsRepositoryTests.swift
@@ -35,7 +35,7 @@ final class UserSettingsRepositoryTests: XCTestCase {
     func testSaveAndGetUserSettings() throws {
         do {
             // Given
-            let userSettings: UserSettings = .init(translationSourceLocale: .english, translationTargetLocale: .korean, hapticsIsOn: true)
+            let userSettings: UserSettings = .init(translationSourceLocale: .english, translationTargetLocale: .korean, hapticsIsOn: true, themeStyle: .system)
 
             // When
             try sut.saveUserSettings(userSettings)
@@ -50,11 +50,12 @@ final class UserSettingsRepositoryTests: XCTestCase {
             XCTAssertEqual(result.translationSourceLocale, .english)
             XCTAssertEqual(result.translationTargetLocale, .korean)
             XCTAssertEqual(result.hapticsIsOn, true)
+            XCTAssertEqual(result.themeStyle, .system)
         }
 
         do {
             // Given
-            let userSettings: UserSettings = .init(translationSourceLocale: .korean, translationTargetLocale: .english, hapticsIsOn: false)
+            let userSettings: UserSettings = .init(translationSourceLocale: .korean, translationTargetLocale: .english, hapticsIsOn: false, themeStyle: .dark)
 
             // When
             try sut.saveUserSettings(userSettings)
@@ -69,6 +70,7 @@ final class UserSettingsRepositoryTests: XCTestCase {
             XCTAssertEqual(result.translationSourceLocale, .korean)
             XCTAssertEqual(result.translationTargetLocale, .english)
             XCTAssertEqual(result.hapticsIsOn, false)
+            XCTAssertEqual(result.themeStyle, .dark)
         }
     }
 
diff --git a/Tests/WordCheckerUITests/Utilities/XCUIApplication+launchEnvironment.swift b/Tests/WordCheckerUITests/Utilities/XCUIApplication+launchEnvironment.swift
index 9de20e5e..efa367c0 100644
--- a/Tests/WordCheckerUITests/Utilities/XCUIApplication+launchEnvironment.swift
+++ b/Tests/WordCheckerUITests/Utilities/XCUIApplication+launchEnvironment.swift
@@ -11,7 +11,7 @@ import XCTest
 
 extension XCUIApplication {
 
-    func setLaunchArguments(_ arguments: [LaunchArguments]) {
+    func setLaunchArguments(_ arguments: [LaunchArgument.Arguments]) {
         self.launchArguments = arguments.map(\.rawValue)
     }
 
diff --git a/Tests/WordCheckerUITests/WordCheckerUITests.swift b/Tests/WordCheckerUITests/WordCheckerUITests.swift
index 9a0b071c..ae0a8d0b 100644
--- a/Tests/WordCheckerUITests/WordCheckerUITests.swift
+++ b/Tests/WordCheckerUITests/WordCheckerUITests.swift
@@ -7,7 +7,7 @@
 
 @testable import Domain
 
-import iOSSupport
+import IOSSupport
 import XCTest
 
 final class WordCheckerUITests: XCTestCase {
diff --git a/Tests/iOSScenesTests/ThemeSettingTests/ThemeSettingTests.swift b/Tests/iOSScenesTests/ThemeSettingTests/ThemeSettingTests.swift
new file mode 100644
index 00000000..52801d12
--- /dev/null
+++ b/Tests/iOSScenesTests/ThemeSettingTests/ThemeSettingTests.swift
@@ -0,0 +1,28 @@
+@testable import ThemeSetting
+
+import XCTest
+
+final class ThemeSettingTests: XCTestCase {
+
+    var sut: ThemeSettingReactor!
+
+    override func setUpWithError() throws {
+        try super.setUpWithError()
+        sut
+    }
+
+    override func tearDownWithError() throws {
+        try super.tearDownWithError()
+        sut = nil
+    }
+
+    func test_example() {
+        // Given
+
+        // When
+
+        // Then
+        XCTAssertEqual("ThemeSettingKit", "ThemeSettingKit")
+    }
+
+}
diff --git a/Tests/iOSScenesTests/UserSettingsTests/UserSettingsReactorTests.swift b/Tests/iOSScenesTests/UserSettingsTests/UserSettingsReactorTests.swift
index 4ee5a153..c28c779c 100644
--- a/Tests/iOSScenesTests/UserSettingsTests/UserSettingsReactorTests.swift
+++ b/Tests/iOSScenesTests/UserSettingsTests/UserSettingsReactorTests.swift
@@ -109,7 +109,7 @@ final class UserSettingsReactorTests: RxBaseTestCase {
     func test_viewDidLoad() {
         // Given
         let userSettingsUseCase: UserSettingsUseCaseFake = .init()
-        userSettingsUseCase.currentUserSettings = .init(translationSourceLocale: .german, translationTargetLocale: .italian, hapticsIsOn: true)
+        userSettingsUseCase.currentUserSettings = .init(translationSourceLocale: .german, translationTargetLocale: .italian, hapticsIsOn: true, themeStyle: .system)
         sut = .init(
             userSettingsUseCase: userSettingsUseCase,
             googleDriveUseCase: GoogleDriveUseCaseFake(scheduler: testScheduler),
diff --git a/Tests/iOSScenesTests/WordCheckingTests/WordCheckingReactorTests.swift b/Tests/iOSScenesTests/WordCheckingTests/WordCheckingReactorTests.swift
index 0f0d0615..8ceaa337 100644
--- a/Tests/iOSScenesTests/WordCheckingTests/WordCheckingReactorTests.swift
+++ b/Tests/iOSScenesTests/WordCheckingTests/WordCheckingReactorTests.swift
@@ -64,4 +64,15 @@ final class WordCheckingReactorTests: XCTestCase {
         XCTAssertNil(sut.currentState.currentWord)
     }
 
+    func test_addDuplicatedWord() {
+        // Given
+        sut.action.onNext(.addWord("testWord"))
+
+        // When
+        sut.action.onNext(.addWord("TESTWORD"))
+
+        // Then
+        XCTAssertNotNil(sut.currentState.showAddCompleteToast)
+    }
+
 }
diff --git a/Tests/iOSScenesTests/WordDetailTests/WordDetailReactorTests.swift b/Tests/iOSScenesTests/WordDetailTests/WordDetailReactorTests.swift
new file mode 100644
index 00000000..25e77149
--- /dev/null
+++ b/Tests/iOSScenesTests/WordDetailTests/WordDetailReactorTests.swift
@@ -0,0 +1,81 @@
+//
+//  WordDetailReactorTests.swift
+//  WordDetailTests
+//
+//  Created by Jaewon Yun on 2/13/24.
+//  Copyright © 2024 woin2ee. All rights reserved.
+//
+
+@testable import WordDetail
+
+import Domain
+import DomainTesting
+import XCTest
+
+final class WordDetailReactorTests: XCTestCase {
+
+    var sut: WordDetailReactor!
+
+    override func tearDownWithError() throws {
+        try super.tearDownWithError()
+        sut = nil
+    }
+
+    func test_enteredWordIsDuplicated() {
+        // Given
+        let uuid1: UUID = .init()
+        let word1: Word = .init(uuid: uuid1, word: "Word1")
+
+        let uuid2: UUID = .init()
+        let word2: Word = .init(uuid: uuid2, word: "Word2")
+
+        let wordUseCase = WordUseCaseFake()
+        wordUseCase._wordList = [word1, word2]
+
+        sut = .init(uuid: word1.uuid, globalAction: .shared, wordUseCase: wordUseCase)
+        sut.action.onNext(.viewDidLoad)
+
+        // When
+        sut.action.onNext(.enteredWord("Word2"))
+
+        // Then
+        XCTAssertTrue(sut.currentState.enteredWordIsDuplicated)
+    }
+
+    func test_enteredWordIsDuplicated_whenSameOriginWord() {
+        // Given
+        let uuid1: UUID = .init()
+        let word1: Word = .init(uuid: uuid1, word: "Word1")
+
+        let wordUseCase = WordUseCaseFake()
+        wordUseCase._wordList = [word1]
+
+        sut = .init(uuid: word1.uuid, globalAction: .shared, wordUseCase: wordUseCase)
+        sut.action.onNext(.viewDidLoad)
+
+        // When
+        sut.action.onNext(.enteredWord("Word1"))
+
+        // Then
+        XCTAssertFalse(sut.currentState.enteredWordIsDuplicated)
+    }
+
+    func test_enteredWordIsEmpty() {
+        // Given
+        let uuid1: UUID = .init()
+        let word1: Word = .init(uuid: uuid1, word: "Word1")
+
+        let wordUseCase = WordUseCaseFake()
+        wordUseCase._wordList = [word1]
+
+        sut = .init(uuid: word1.uuid, globalAction: .shared, wordUseCase: wordUseCase)
+        sut.action.onNext(.viewDidLoad)
+
+        // When
+        sut.action.onNext(.enteredWord(""))
+
+        // Then
+        XCTAssertTrue(sut.currentState.enteredWordIsEmpty)
+    }
+
+}
diff --git a/Tuist/Dependencies.swift b/Tuist/Dependencies.swift
index bc6f36d4..4b574472 100644
--- a/Tuist/Dependencies.swift
+++ b/Tuist/Dependencies.swift
@@ -43,6 +43,9 @@ let dependencies = Dependencies(
         // ReactorKit
         .remote(url: "https://github.com/ReactorKit/ReactorKit.git",
                 requirement: .upToNextMajor(from: "3.0.0")),
+        // ReactorKit
+        .remote(url: "https://github.com/Woin2ee-Modules/FoundationPlus.git",
+                requirement: .upToNextMajor(from: "1.0.0")),
     ],
     platforms: [.iOS]
 )
diff --git a/Tuist/ProjectDescriptionHelpers/ExternalDependencyName.swift b/Tuist/ProjectDescriptionHelpers/ExternalDependencyName.swift
index c061ab3b..1607f572 100644
--- a/Tuist/ProjectDescriptionHelpers/ExternalDependencyName.swift
+++ b/Tuist/ProjectDescriptionHelpers/ExternalDependencyName.swift
@@ -23,5 +23,6 @@ public struct ExternalDependencyName {
     public static let googleAPIClientForRESTCore = "GoogleAPIClientForRESTCore"
     public static let reactorKit = "ReactorKit"
     public static let swiftCollections = "Collections"
+    public static let foundationPlus = "FoundationPlus"
 
 }
diff --git a/Tuist/Templates/Assembly.stencil b/Tuist/Templates/Assembly.stencil
index 6aec4c96..625e07a0 100644
--- a/Tuist/Templates/Assembly.stencil
+++ b/Tuist/Templates/Assembly.stencil
@@ -7,6 +7,10 @@ public final class {{ name }}Assembly: Assembly {
     public init() {}
 
     public func assemble(container: Container) {
+        container.register({{ name }}Reactor.self) { _ in
+            return {{ name }}Reactor.init()
+        }
+
         container.register({{ name }}ViewControllerProtocol.self) { resolver in
             return {{ name }}ViewController().then {
                 $0.reactor = resolver.resolve()
diff --git a/Tuist/Templates/iOSScene/iOSScene.swift b/Tuist/Templates/IOSScene/IOSScene.swift
similarity index 68%
rename from Tuist/Templates/iOSScene/iOSScene.swift
rename to Tuist/Templates/IOSScene/IOSScene.swift
index c65cce74..5a5609df 100644
--- a/Tuist/Templates/iOSScene/iOSScene.swift
+++ b/Tuist/Templates/IOSScene/IOSScene.swift
@@ -3,30 +3,30 @@ import ProjectDescription
 let nameAttribute: Template.Attribute = .required("name")
 
 let template = Template(
-    description: "Create default files for iOSScene.",
+    description: "Create default files for IOSScene.",
     attributes: [
         nameAttribute,
         .optional("platform", default: "ios"),
     ],
     items: [
         .file(
-            path: "Sources/iOSScenes/\(nameAttribute)/\(nameAttribute)ViewController.swift",
+            path: "Sources/IOSScenes/\(nameAttribute)/\(nameAttribute)ViewController.swift",
             templatePath: .relativeToCurrentFile("../ViewController.stencil")
         ),
         .file(
-            path: "Sources/iOSScenes/\(nameAttribute)/\(nameAttribute)Reactor.swift",
+            path: "Sources/IOSScenes/\(nameAttribute)/\(nameAttribute)Reactor.swift",
             templatePath: .relativeToCurrentFile("../Reactor.stencil")
         ),
         .file(
-            path: "Sources/iOSScenes/\(nameAttribute)/\(nameAttribute)Assembly.swift",
+            path: "Sources/IOSScenes/\(nameAttribute)/\(nameAttribute)Assembly.swift",
             templatePath: .relativeToCurrentFile("../Assembly.stencil")
         ),
         .file(
-            path: "Sources/iPhoneDriver/Coordinators/\(nameAttribute)Coordinator.swift",
-            templatePath: .relativeToCurrentFile("../iPhoneCoordinator.stencil")
+            path: "Sources/IPhoneDriver/Coordinators/\(nameAttribute)Coordinator.swift",
+            templatePath: .relativeToCurrentFile("../IPhoneCoordinator.stencil")
         ),
         .file(
-            path: "Tests/iOSScenesTests/\(nameAttribute)Tests/\(nameAttribute)Tests.swift",
+            path: "Tests/IOSScenesTests/\(nameAttribute)Tests/\(nameAttribute)Tests.swift",
             templatePath: .relativeToCurrentFile("../UnitTests.stencil")
         ),
         .file(
diff --git a/Tuist/Templates/Reactor.stencil b/Tuist/Templates/Reactor.stencil
index 26bc13be..4ab37f40 100644
--- a/Tuist/Templates/Reactor.stencil
+++ b/Tuist/Templates/Reactor.stencil
@@ -18,15 +18,15 @@ final class {{ name }}Reactor: Reactor {
 
     func mutate(action: Action) -> Observable<Mutation> {
         switch action {
-            
+
         }
     }
 
     func reduce(state: State, mutation: Mutation) -> State {
         var state = state
-        
+
         switch mutation {
-            
+
         }
 
         return state
diff --git a/Tuist/Templates/UnitTests.stencil b/Tuist/Templates/UnitTests.stencil
index be775c69..b369e3b9 100644
--- a/Tuist/Templates/UnitTests.stencil
+++ b/Tuist/Templates/UnitTests.stencil
@@ -4,7 +4,7 @@ import XCTest
 
 final class {{ name }}Tests: XCTestCase {
 
-    var sut: <#Code#>!
+    var sut: {{ name }}Reactor!
 
     override func setUpWithError() throws {
         try super.setUpWithError()
@@ -15,16 +15,14 @@ final class {{ name }}Tests: XCTestCase {
         try super.tearDownWithError()
         sut = nil
     }
-    
+
     func test_example() {
         // Given
-        
-        
+
         // When
-        
-        
+
         // Then
         XCTAssertEqual("{{ name }}Kit", "{{ name }}Kit")
     }
-    
+
 }
diff --git a/Tuist/Templates/ViewController.stencil b/Tuist/Templates/ViewController.stencil
index 81bc5333..7e1ece88 100644
--- a/Tuist/Templates/ViewController.stencil
+++ b/Tuist/Templates/ViewController.stencil
@@ -1,10 +1,8 @@
-import iOSSupport
+import IOSSupport
 import ReactorKit
 import UIKit
 
-public protocol {{ name }}ViewControllerDelegate: AnyObject {
-    // An example if you use navigation stack.
-    func willPopView()
+public protocol {{ name }}ViewControllerDelegate: AnyObject, ViewControllerDelegate {
 }
 
 public protocol {{ name }}ViewControllerProtocol: UIViewController {
diff --git a/Tuist/Templates/iPhoneCoordinator.stencil b/Tuist/Templates/iPhoneCoordinator.stencil
new file mode 100644
index 00000000..22dbac7b
--- /dev/null
+++ b/Tuist/Templates/iPhoneCoordinator.stencil
@@ -0,0 +1,26 @@
+import IOSSupport
+import SwinjectDIContainer
+import SwinjectExtension
+import UIKit
+
+import {{ name }}
+
+final class {{ name }}Coordinator: BasicCoordinator {
+
+    override func start() {
+        // An example if you push view controller.
+        let viewController: {{ name }}ViewControllerProtocol = DIContainer.shared.resolver.resolve()
+        viewController.delegate = self
+        navigationController.pushViewController(viewController, animated: true)
+    }
+
+    /* If you want start to coordinator with arguments.
+    func start<Arg1>(with argument: Arg1) {
+
+    }
+    */
+
+}
+
+extension {{ name }}Coordinator: {{ name }}ViewControllerDelegate {
+}
diff --git a/Tuist/Templates/iPhoneCoorinator.stencil b/Tuist/Templates/iPhoneCoorinator.stencil
deleted file mode 100644
index e5564921..00000000
--- a/Tuist/Templates/iPhoneCoorinator.stencil
+++ /dev/null
@@ -1,41 +0,0 @@
-import iOSSupport
-import SwinjectDIContainer
-import SwinjectExtension
-import UIKit
-import {{ name }}
-
-final class {{ name }}Coordinator: Coordinator {
-
-    weak var parentCoordinator: Coordinator?
-    var childCoordinators: [Coordinator] = []
-
-    let navigationController: UINavigationController
-
-    init(navigationController: UINavigationController) {
-        self.navigationController = navigationController
-    }
-
-    func start() {
-        // An example if you use navigation stack.
-        let viewController: {{ name }}ViewControllerProtocol = DIContainer.shared.resolver.resolve()
-        viewController.delegate = self
-        navigationController.pushViewController(viewController, animated: true)
-    }
-    
-    /* If you want start to coordinator with arguments.
-    func start<Arg1>(with argument: Arg1) {
-        
-    }
-    */
-
-}
-
-extension {{ name }}Coordinator: {{ name }}ViewControllerDelegate {
-
-    // An example if you use navigation stack.
-    func willPopView() {
-        navigationController.popViewController(animated: true)
-        parentCoordinator?.childCoordinators.removeAll(where: { $0 === self })
-    }
-
-}
diff --git a/graph.png b/graph.png
index 08753928..9479a285 100644
Binary files a/graph.png and b/graph.png differ