diff --git a/src/Aggregate.ts b/src/Aggregate.ts
index e37f88b..adbb8af 100644
--- a/src/Aggregate.ts
+++ b/src/Aggregate.ts
@@ -41,11 +41,11 @@ import {
 } from '@/Entity'
 
 import {
-  EventTopics,
-  EventObservable,
-} from '@/Event'
+  MessageTopics,
+  MessageObservable,
+} from '@/Message'
 
-export abstract class Aggregate<E extends Entity, T extends EventTopics = EventTopics> extends EventObservable<T> {
+export abstract class Aggregate<E extends Entity, T extends MessageTopics = MessageTopics> extends MessageObservable<T> {
   protected root: E
 
   constructor(root: E) {
diff --git a/src/Event.ts b/src/Event.ts
index 8fb60a1..2187bbe 100644
--- a/src/Event.ts
+++ b/src/Event.ts
@@ -36,13 +36,16 @@
 
 import {
   guard,
-  FoundationError,
 } from '@cosmicmind/foundationjs'
 
 import {
-  Observable,
-  ObservableTopics,
-} from '@cosmicmind/patternjs'
+  Message,
+  MessageError,
+  MessageLifecycle,
+  MessagePropertyKey,
+  MessagePropertyLifecycle,
+  MessagePropertyLifecycleMap,
+} from '@/Message'
 
 /**
  * Represents an Event.
@@ -53,70 +56,17 @@ import {
  *   age: 25
  * }
  */
-export type Event = Record<string, unknown>
+export type Event = Message
 
-/**
- * Represents a collection of event topics.
- *
- * @extends {ObservableTopics}
- *
- * @property {Event} [K] - The event topic.
- */
-export type EventTopics = ObservableTopics & {
-  readonly [K: string]: Event
-}
-
-/**
- * An observable class for handling events of specific types.
- *
- * @template T The event topic type.
- */
-export class EventObservable<T extends EventTopics> extends Observable<T> {}
-
-/**
- * Represents a type that is a valid property key of a given event type.
- *
- * @template K - The event type.
- * @typeparam K - A type is a valid property key.
- *
- * @returns - A valid property key of the event type, or `never` if the key is not a valid property key.
- */
-export type EventPropertyKey<K> = keyof K extends string | symbol ? keyof K : never
+export type EventPropertyKey<K> = MessagePropertyKey<K>
 
-/**
- * Represents the lifecycle hooks for an event property.
- *
- * @template E - The type of the event.
- * @template V - The type of the property value.
- */
-export type EventPropertyLifecycle<E extends Event, V> = {
-  required?: boolean
-  validator?(value: V, event: E): boolean | never
-  updated?(newValue: V, oldValue: V, event: E): void
-}
+export type EventPropertyLifecycle<E extends Event, V> = MessagePropertyLifecycle<E, V>
 
-/**
- * Represents a map that defines the lifecycle of event properties.
- *
- * @template E - The type of the event.
- */
-export type EventPropertyLifecycleMap<E extends Event> = {
-  [K in keyof E]?: EventPropertyLifecycle<E, E[K]>
-}
+export type EventPropertyLifecycleMap<E extends Event> = MessagePropertyLifecycleMap<E>
 
-export class EventError extends FoundationError {}
+export class EventError extends MessageError {}
 
-/**
- * Represents the lifecycle methods for an event.
- *
- * @template E - The type of event.
- */
-export type EventLifecycle<E extends Event> = {
-  created?(event: E): void
-  trace?(event: E): void
-  error?(error: EventError): void
-  properties?: EventPropertyLifecycleMap<E>
-}
+export type EventLifecycle<E extends Event> = MessageLifecycle<E>
 
 /**
  * Defines an event with an optional event lifecycle handler.
diff --git a/src/Message.ts b/src/Message.ts
new file mode 100644
index 0000000..e52f3af
--- /dev/null
+++ b/src/Message.ts
@@ -0,0 +1,215 @@
+/**
+ * BSD 3-Clause License
+ *
+ * Copyright © 2023, Daniel Jonathan <daniel at cosmicmind dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES LOSS OF USE, DATA, OR PROFITS OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @module Message
+ */
+
+import {
+  guard,
+  FoundationError,
+} from '@cosmicmind/foundationjs'
+
+import {
+  Observable,
+  ObservableTopics,
+} from '@cosmicmind/patternjs'
+
+/**
+ * Represents an Message.
+ *
+ * @example
+ * const message: Message = {
+ *   name: 'John Doe',
+ *   age: 25
+ * }
+ */
+export type Message = Record<string, unknown>
+
+/**
+ * Represents a collection of message topics.
+ *
+ * @extends {ObservableTopics}
+ *
+ * @property {Message} [K] - The message topic.
+ */
+export type MessageTopics = ObservableTopics & {
+  readonly [K: string]: Message
+}
+
+/**
+ * An observable class for handling messages of specific types.
+ *
+ * @template T The message topic type.
+ */
+export class MessageObservable<T extends MessageTopics> extends Observable<T> {}
+
+/**
+ * Represents a type that is a valid property key of a given message type.
+ *
+ * @template K - The message type.
+ * @typeparam K - A type is a valid property key.
+ *
+ * @returns - A valid property key of the message type, or `never` if the key is not a valid property key.
+ */
+export type MessagePropertyKey<K> = keyof K extends string | symbol ? keyof K : never
+
+/**
+ * Represents the lifecycle hooks for an message property.
+ *
+ * @template E - The type of the message.
+ * @template V - The type of the property value.
+ */
+export type MessagePropertyLifecycle<E extends Message, V> = {
+  required?: boolean
+  validator?(value: V, message: E): boolean | never
+  updated?(newValue: V, oldValue: V, message: E): void
+}
+
+/**
+ * Represents a map that defines the lifecycle of message properties.
+ *
+ * @template E - The type of the message.
+ */
+export type MessagePropertyLifecycleMap<E extends Message> = {
+  [K in keyof E]?: MessagePropertyLifecycle<E, E[K]>
+}
+
+export class MessageError extends FoundationError {}
+
+/**
+ * Represents the lifecycle methods for an message.
+ *
+ * @template E - The type of message.
+ */
+export type MessageLifecycle<E extends Message> = {
+  created?(message: E): void
+  trace?(message: E): void
+  error?(error: MessageError): void
+  properties?: MessagePropertyLifecycleMap<E>
+}
+
+/**
+ * Defines an message with an optional message lifecycle handler.
+ *
+ * @template E The type of the message.
+ * @param {MessageLifecycle<E>} [handler={}] The optional message lifecycle handler.
+ * @returns {(message: E) => E} A function that creates an message with the given lifecycle handler.
+ */
+export const defineMessage = <E extends Message>(handler: MessageLifecycle<E> = {}): (message: E) => E =>
+  (message: E): E => createMessage(message, handler)
+
+/**
+ * Creates a ProxyHandler for Message instances with the given MessageLifecycle handler.
+ * The ProxyHandler intercepts property set operations, validates the new value against the associated property validator,
+ * triggers the updated callback for the property, updates the property value, and traces the change if trace is enabled.
+ *
+ * @typeparam E - The type of Message.
+ * @param handler - The MessageLifecycle handler.
+ * @returns A ProxyHandler for Message instances.
+ */
+function createMessageHandler<E extends Message>(handler: MessageLifecycle<E>): ProxyHandler<E> {
+  return {
+    set<A extends MessagePropertyKey<E>, V extends E[A]>(target: E, key: A, value: V): boolean | never {
+      const property = handler.properties?.[key]
+
+      if (false === property?.validator?.(value, target)) {
+        throwErrorAndTrace(`${JSON.stringify(target)} ${String(key)} is invalid`, handler)
+      }
+
+      property?.updated?.(value, target[key], target)
+
+      const result = Reflect.set(target, key, value)
+      handler.trace?.(target)
+
+      return result
+    },
+  }
+}
+
+/**
+ * Throws an MessageError with a specified message and invokes the error handler.
+ *
+ * @template E - The type of Message.
+ * @param {string} message - The error message.
+ * @param {MessageLifecycle<E>} handler - The message lifecycle handler.
+ * @throws {MessageError} - The MessageError instance.
+ * @return {never} - This method never returns.
+ */
+function throwErrorAndTrace<E extends Message>(message: string, handler: MessageLifecycle<E>): never {
+  const error = new MessageError(message)
+  handler.error?.(error)
+  throw error
+}
+
+/**
+ * Creates an message of type `E`.
+ *
+ * @template E - The type of the message to create.
+ * @param {E} target - The target object to create the message from.
+ * @param {MessageLifecycle<E>} [handler={}] - The lifecycle handler for the message.
+ * @returns {E} - The created message object.
+ * @throws {MessageError} - If the target object is invalid.
+ */
+function createMessage<E extends Message>(target: E, handler: MessageLifecycle<E> = {}): E | never {
+  if (guard<E>(target)) {
+    const properties = handler.properties
+
+    if (guard<MessagePropertyLifecycleMap<E>>(properties)) {
+      const message = new Proxy(target, createMessageHandler(handler))
+
+      for (const [ key, property ] of Object.entries(properties) as [string, MessagePropertyLifecycle<E, unknown>][]) {
+        if (property.required) {
+          if (!(key in target)) {
+            throwErrorAndTrace(`${JSON.stringify(target)} ${key} is required`, handler)
+          }
+
+          if (false === property.validator?.(target[key], message)) {
+            throwErrorAndTrace(`${JSON.stringify(target)} ${key} is invalid`, handler)
+          }
+        }
+        else if (key in target && 'undefined' !== typeof target[key]) {
+          if (guard(property, 'validator') && false === property.validator?.(target[key], message)) {
+            throwErrorAndTrace(`${JSON.stringify(target)} ${key} is invalid`, handler)
+          }
+        }
+      }
+
+      handler.created?.(message)
+      handler.trace?.(message)
+
+      return message
+    }
+  }
+
+  throw new MessageError(`${String(target)} is invalid`)
+}
\ No newline at end of file
diff --git a/src/Topic.ts b/src/Topic.ts
new file mode 100644
index 0000000..92b92bd
--- /dev/null
+++ b/src/Topic.ts
@@ -0,0 +1,62 @@
+/**
+ * BSD 3-Clause License
+ *
+ * Copyright © 2023, Daniel Jonathan <daniel at cosmicmind dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES LOSS OF USE, DATA, OR PROFITS OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @module Topic
+ */
+
+import {
+  Observable,
+  ObservableTopics,
+} from '@cosmicmind/patternjs'
+
+import {
+  Message,
+} from '@/Message'
+
+/**
+ * Represents a collection of Message topics.
+ *
+ * @extends {ObservableTopics}
+ *
+ * @property {Message} [K] - A message topic.
+ */
+export type MessageTopics = ObservableTopics & {
+  readonly [K: string]: Message
+}
+
+/**
+ * An observable class for handling topics of specific types.
+ *
+ * @template T The message topic type.
+ */
+export class TopicObservable<T extends MessageTopics> extends Observable<T> {}
diff --git a/src/index.ts b/src/index.ts
index c7aa9de..4972f9e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -32,7 +32,6 @@
 
 export * from '@/Aggregate'
 export * from '@/Event'
-export * from '@/Event'
-export * from '@/Entity'
 export * from '@/Entity'
+export * from '@/Message'
 export * from '@/Value'
\ No newline at end of file