diff --git a/Library/ExternalInvoice.cs b/Library/ExternalInvoice.cs
index ed28a1b4..cd5d80e7 100644
--- a/Library/ExternalInvoice.cs
+++ b/Library/ExternalInvoice.cs
@@ -34,6 +34,15 @@ public ExternalSubscription ExternalSubscription
             internal set { _externalSubscription = value; }
         }
 
+        private string _externalPaymentPhaseUuid;
+        public string ExternalPaymentPhaseUuid => _externalPaymentPhaseUuid;
+
+        private ExternalPaymentPhase _externalPaymentPhase;
+        public ExternalPaymentPhase ExternalPaymentPhase
+        {
+            get { return _externalPaymentPhase ?? (_externalPaymentPhase = ExternalPaymentPhases.Get(_externalPaymentPhaseUuid)); }
+            internal set { _externalPaymentPhase = value; }
+        }
         public string ExternalId { get; private set; }
         public ExternalInvoiceState State { get; private set; }
         public decimal Total { get; private set; }
@@ -86,6 +95,12 @@ internal override void ReadXml(XmlTextReader reader)
                             _externalSubscriptionUuid = Uri.UnescapeDataString(href.Substring(href.LastIndexOf("/") + 1));
                         break;
 
+                    case "external_payment_phase":
+                        href = reader.GetAttribute("href");
+                        if (null != href)
+                            _externalPaymentPhaseUuid = Uri.UnescapeDataString(href.Substring(href.LastIndexOf("/") + 1));
+                        break;
+
                     case "external_id":
                         ExternalId = reader.ReadElementContentAsString();
                         break;
diff --git a/Library/ExternalPaymentPhase.cs b/Library/ExternalPaymentPhase.cs
new file mode 100644
index 00000000..2b55ec2c
--- /dev/null
+++ b/Library/ExternalPaymentPhase.cs
@@ -0,0 +1,154 @@
+using System;
+using System.Net;
+using System.Xml;
+
+namespace Recurly
+{
+    public class ExternalPaymentPhase : RecurlyEntity
+    {
+        public DateTime StartedAt { get; private set; }
+        public DateTime EndsAt { get; private set; }
+        public int StartingBillingPeriodIndex { get; private set; }
+        public int EndingBillingPeriodIndex { get; private set; }
+        public string OfferType { get; private set; }
+        public string OfferName { get; private set; }
+        public int PeriodCount { get; private set; }
+        public string PeriodLength { get; private set; }
+        public decimal Amount { get; private set; }
+        public string Currency { get; private set; }
+        public DateTime CreatedAt { get; private set; }
+        public DateTime UpdatedAt { get; private set; }
+
+        internal const string UrlPrefix = "/external_payment_phases/";
+
+        internal ExternalPaymentPhase()
+        {
+        }
+        internal ExternalPaymentPhase(XmlTextReader reader)
+        {
+            ReadXml(reader);
+        }
+        #region Read XML documents
+
+        internal override void ReadXml(XmlTextReader reader)
+        {
+            while (reader.Read())
+            {
+                DateTime dateVal;
+
+                if (reader.Name == "external_payment_phase" && reader.NodeType == XmlNodeType.EndElement)
+                    break;
+
+                if (reader.NodeType != XmlNodeType.Element) continue;
+
+                switch (reader.Name)
+                {
+                    case "started_at":
+                        if (DateTime.TryParse(reader.ReadElementContentAsString(), out dateVal))
+                            StartedAt = dateVal; ;
+                        break;
+
+                    case "ends_at":
+                        if (DateTime.TryParse(reader.ReadElementContentAsString(), out dateVal))
+                            EndsAt = dateVal; ;
+                        break;
+
+                    case "starting_billing_period_index":
+                        StartingBillingPeriodIndex = reader.ReadElementContentAsInt();
+                        break;
+
+                    case "ending_billing_period_index":
+                        EndingBillingPeriodIndex = reader.ReadElementContentAsInt();
+                        break;
+
+                    case "offer_type":
+                        OfferType = reader.ReadElementContentAsString();
+                        break;
+
+                    case "offer_name":
+                        OfferName = reader.ReadElementContentAsString();
+                        break;
+
+                    case "period_count":
+                        PeriodCount = reader.ReadElementContentAsInt();
+                        break;
+
+                    case "period_length":
+                        PeriodLength = reader.ReadElementContentAsString();
+                        break;
+
+                    case "amount":
+                        Amount = reader.ReadElementContentAsDecimal();
+                        break;
+
+                    case "currency":
+                        Currency = reader.ReadElementContentAsString();
+                        break;
+
+                    case "updated_at":
+                        if (DateTime.TryParse(reader.ReadElementContentAsString(), out dateVal))
+                            UpdatedAt = dateVal; ;
+                        break;
+
+                    case "created_at":
+                        if (DateTime.TryParse(reader.ReadElementContentAsString(), out dateVal))
+                            CreatedAt = dateVal; ;
+                        break;
+
+                }
+            }
+        }
+
+        internal override void WriteXml(XmlTextWriter writer)
+        {
+            throw new NotImplementedException();
+        }
+
+        #endregion
+
+        #region Object Overrides
+
+        public override string ToString()
+        {
+            return "Recurly External Payment Phase: " + StartedAt + " " + EndsAt + " " + StartingBillingPeriodIndex + " " + EndingBillingPeriodIndex + " " + OfferType + " " + OfferName + " " + PeriodCount + " " + PeriodLength + " " + Amount + " " + Currency + " " + CreatedAt + " " + UpdatedAt;
+        }
+
+        #endregion
+    }
+
+    public sealed class ExternalPaymentPhases
+    {
+        /// <summary>
+        /// Returns a list of recurly external_payment_phases
+        /// </summary>
+        /// <returns></returns>
+        public static RecurlyList<ExternalPaymentPhase> List()
+        {
+            return List(null);
+        }
+        /// <summary>
+        /// Returns a list of recurly external_payment_phases
+        /// </summary>
+        /// <param name="filter">FilterCriteria used to apply server side sorting and filtering</param>
+        /// <returns></returns>
+        public static RecurlyList<ExternalPaymentPhase> List(FilterCriteria filter)
+        {
+            filter = filter ?? FilterCriteria.Instance;
+            var parameters = filter.ToNamedValueCollection();
+            return new ExternalPaymentPhaseList(ExternalPaymentPhase.UrlPrefix + "?" + parameters.ToString());
+        }
+        public static ExternalPaymentPhase Get(string uuid)
+        {
+            if (string.IsNullOrWhiteSpace(uuid))
+            {
+                return null;
+            }
+            var externalPaymentPhase = new ExternalPaymentPhase();
+            var statusCode = Client.Instance.PerformRequest(Client.HttpRequestMethod.Get,
+                ExternalPaymentPhase.UrlPrefix + Uri.EscapeDataString(uuid),
+                externalPaymentPhase.ReadXml);
+
+            return statusCode == HttpStatusCode.NotFound ? null : externalPaymentPhase;
+        }
+    }
+}
diff --git a/Library/ExternalSubscription.cs b/Library/ExternalSubscription.cs
index 661b81e3..1e1082bb 100644
--- a/Library/ExternalSubscription.cs
+++ b/Library/ExternalSubscription.cs
@@ -21,6 +21,12 @@ public Account Account
             internal set { _account = value; }
         }
 
+        private List<ExternalInvoice> _externalInvoices;
+        public List<ExternalInvoice> ExternalInvoices
+        {
+            get { return _externalInvoices ?? (_externalInvoices = new List<ExternalInvoice>()); }
+            set { _externalInvoices = value; }
+        }
         public string ExternalId { get; set; }
         public string AppIdentifier { get; private set; }
         public string State { get; set; }
@@ -204,5 +210,33 @@ public static RecurlyList<ExternalInvoice> GetExternalInvoices(string uuid)
         {
             return new ExternalInvoiceList(ExternalSubscription.UrlPrefix + Uri.EscapeDataString(uuid) + "/external_invoices/");
         }
+
+        /// <summary>
+        /// Returns a list of external_payment_phases for this external subscription
+        /// </summary>
+        /// <returns></returns>
+        public static RecurlyList<ExternalPaymentPhase> GetExternalPaymentPhases(string uuid)
+        {
+            return new ExternalPaymentPhaseList(ExternalSubscription.UrlPrefix + Uri.EscapeDataString(uuid) + ExternalPaymentPhase.UrlPrefix);
+        }
+
+        /// <summary>
+        /// Returns an external payment phase for external subscription
+        /// </summary>
+        /// <returns></returns>
+        public static ExternalPaymentPhase GetExternalPaymentPhase(string uuid, string externalPaymentPhaseUuid)
+        {
+            if (string.IsNullOrWhiteSpace(uuid) || string.IsNullOrWhiteSpace(externalPaymentPhaseUuid))
+            {
+                return null;
+            }
+            var externalPaymentPhase = new ExternalPaymentPhase();
+            var statusCode = Client.Instance.PerformRequest(Client.HttpRequestMethod.Get,
+                ExternalSubscription.UrlPrefix + Uri.EscapeDataString(uuid) + ExternalPaymentPhase.UrlPrefix + Uri.EscapeDataString(externalPaymentPhaseUuid),
+                externalPaymentPhase.ReadXml);
+
+            return statusCode == HttpStatusCode.NotFound ? null : externalPaymentPhase;
+        }
+
     }
 }
diff --git a/Library/List/ExternalInvoiceList.cs b/Library/List/ExternalInvoiceList.cs
index c8998658..ff59b92f 100644
--- a/Library/List/ExternalInvoiceList.cs
+++ b/Library/List/ExternalInvoiceList.cs
@@ -8,6 +8,9 @@ internal ExternalInvoiceList(string baseUrl) : base(Client.HttpRequestMethod.Get
         {
         }
 
+        internal ExternalInvoiceList()
+        {
+        }
         public override RecurlyList<ExternalInvoice> Start
         {
             get { return HasStartPage() ? new ExternalInvoiceList(StartUrl) : RecurlyList.Empty<ExternalInvoice>(); }
diff --git a/Library/List/ExternalPaymentPhaseList.cs b/Library/List/ExternalPaymentPhaseList.cs
new file mode 100644
index 00000000..7a652532
--- /dev/null
+++ b/Library/List/ExternalPaymentPhaseList.cs
@@ -0,0 +1,43 @@
+using System.Xml;
+
+namespace Recurly
+{
+    public class ExternalPaymentPhaseList : RecurlyList<ExternalPaymentPhase>
+    {
+        internal ExternalPaymentPhaseList(string baseUrl) : base(Client.HttpRequestMethod.Get, baseUrl)
+        {
+        }
+
+        internal ExternalPaymentPhaseList()
+        {
+        }
+        public override RecurlyList<ExternalPaymentPhase> Start
+        {
+            get { return HasStartPage() ? new ExternalPaymentPhaseList(StartUrl) : RecurlyList.Empty<ExternalPaymentPhase>(); }
+        }
+
+        public override RecurlyList<ExternalPaymentPhase> Next
+        {
+            get { return HasNextPage() ? new ExternalPaymentPhaseList(NextUrl) : RecurlyList.Empty<ExternalPaymentPhase>(); }
+        }
+
+        public override RecurlyList<ExternalPaymentPhase> Prev
+        {
+            get { return HasPrevPage() ? new ExternalPaymentPhaseList(PrevUrl) : RecurlyList.Empty<ExternalPaymentPhase>(); }
+        }
+
+        internal override void ReadXml(XmlTextReader reader)
+        {
+            while (reader.Read())
+            {
+                if (reader.Name == "external_payment_phases" && reader.NodeType == XmlNodeType.EndElement)
+                    break;
+
+                if (reader.NodeType == XmlNodeType.Element && reader.Name == "external_payment_phase")
+                {
+                    Add(new ExternalPaymentPhase(reader));
+                }
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Test/ExternalInvoiceTest.cs b/Test/ExternalInvoiceTest.cs
index e0fca1dd..583fb004 100644
--- a/Test/ExternalInvoiceTest.cs
+++ b/Test/ExternalInvoiceTest.cs
@@ -1,7 +1,7 @@
 using System;
-using System.Collections.Generic;
+using System.Xml;
 using FluentAssertions;
-using Xunit;
+using Recurly.Test.Fixtures;
 
 namespace Recurly.Test
 {
@@ -10,12 +10,16 @@ public class ExternalInvoiceTest : BaseTest
         [RecurlyFact(TestEnvironment.Type.Integration)]
         public void LookupExternalInvoice()
         {
-            var uuid = "sl7984v66da8";
-            var externalInvoice = ExternalInvoices.Get(uuid);
-            externalInvoice.ExternalId.Should().Be("external_id");
+            var xmlFixture = FixtureImporter.Get(FixtureType.ExternalInvoices, "show-200").Xml;
+            XmlTextReader reader = new XmlTextReader(new System.IO.StringReader(xmlFixture));
+            var externalInvoice = new ExternalInvoice();
+            externalInvoice.ReadXml(reader);
+            externalInvoice.ExternalId.Should().Be("2000000458276005");
             externalInvoice.State.Should().Be(ExternalInvoice.ExternalInvoiceState.Paid);
-            externalInvoice.Total.Should().Be(123);
+            externalInvoice.Total.Should().Be(new decimal(10.45));
             externalInvoice.Currency.Should().Be("USD");
+            externalInvoice.ExternalSubscriptionUuid.Should().Be("tsfnx2vn5wh6");
+            externalInvoice.ExternalPaymentPhaseUuid.Should().Be("twqswp627ri3");
             externalInvoice.PurchasedAt.Should().NotBe(default(DateTime));
             externalInvoice.CreatedAt.Should().NotBe(default(DateTime));
             externalInvoice.UpdatedAt.Should().NotBe(default(DateTime));
diff --git a/Test/ExternalPaymentPhaseTest.cs b/Test/ExternalPaymentPhaseTest.cs
new file mode 100644
index 00000000..4091d766
--- /dev/null
+++ b/Test/ExternalPaymentPhaseTest.cs
@@ -0,0 +1,31 @@
+using System;
+using System.Xml;
+using FluentAssertions;
+using Recurly.Test.Fixtures;
+
+namespace Recurly.Test
+{
+    public class ExternalPaymentPhaseTest : BaseTest
+    {
+        [RecurlyFact(TestEnvironment.Type.Integration)]
+        public void LookupExternalPaymentPhase()
+        {
+            var externalPaymentPhase = new ExternalPaymentPhase();
+            var xmlFixture = FixtureImporter.Get(FixtureType.ExternalPaymentPhases, "show-200").Xml;
+            XmlTextReader reader = new XmlTextReader(new System.IO.StringReader(xmlFixture));
+            externalPaymentPhase.ReadXml(reader);
+            externalPaymentPhase.StartedAt.Should().Be(new DateTime(2023, 11, 15, 0, 0, 0, DateTimeKind.Utc));
+            externalPaymentPhase.EndsAt.Should().Be(new DateTime(2023, 11, 17, 21, 27, 10, DateTimeKind.Utc));
+            externalPaymentPhase.StartingBillingPeriodIndex.Should().Be(1);
+            externalPaymentPhase.EndingBillingPeriodIndex.Should().Be(2);
+            externalPaymentPhase.OfferType.Should().Be("FREE_TRIAL");
+            externalPaymentPhase.OfferName.Should().Be("introductory");
+            externalPaymentPhase.PeriodCount.Should().Be(2);
+            externalPaymentPhase.PeriodLength.Should().Be("TWO WEEKS");
+            externalPaymentPhase.Amount.Should().Be(new decimal(1.99));
+            externalPaymentPhase.Currency.Should().Be("USD");
+            externalPaymentPhase.CreatedAt.Should().Be(new DateTime(2023, 11, 15, 16, 16, 43, DateTimeKind.Utc));
+            externalPaymentPhase.UpdatedAt.Should().Be(new DateTime(2023, 11, 15, 16, 16, 43, DateTimeKind.Utc));
+        }
+    }
+}
diff --git a/Test/Fixtures/FixtureImporter.cs b/Test/Fixtures/FixtureImporter.cs
index bb4a64ae..b01b30db 100644
--- a/Test/Fixtures/FixtureImporter.cs
+++ b/Test/Fixtures/FixtureImporter.cs
@@ -8,6 +8,15 @@ namespace Recurly.Test.Fixtures
 {
     public class FixtureImporter
     {
+        public static string GetFixtureTypeDescription(FixtureType type)
+        {
+            DescriptionAttribute[] attributes = (DescriptionAttribute[])type
+           .GetType()
+           .GetField(type.ToString())
+           .GetCustomAttributes(typeof(DescriptionAttribute), false);
+
+            return attributes.Length > 0 ? attributes[0].Description : string.Empty;
+        }
         public static FixtureResponse Get(FixtureType type, string name)
         {
             if (name.IsNullOrEmpty())
@@ -16,7 +25,7 @@ public static FixtureResponse Get(FixtureType type, string name)
             if (!Enum.IsDefined(typeof(FixtureType), type))
                 throw new InvalidEnumArgumentException("type", (int)type, typeof(FixtureType));
 
-            var fixturePath = string.Format("fixtures/{0}/{1}.xml", type, name);
+            var fixturePath = string.Format("Fixtures/{0}/{1}.xml", GetFixtureTypeDescription(type), name);
 
             if (!File.Exists(fixturePath))
                 throw new FileNotFoundException("Could not locate the fixture response file!", fixturePath);
@@ -66,6 +75,10 @@ private static KeyValuePair<string, string> ParseHeader(string line)
 
     public enum FixtureType
     {
-        Accounts
+        Accounts,
+        [Description("external_payment_phases")]
+        ExternalPaymentPhases,
+        [Description("external_invoices")]
+        ExternalInvoices,
     }
 }
diff --git a/Test/Fixtures/external_invoices/index-200.xml b/Test/Fixtures/external_invoices/index-200.xml
new file mode 100644
index 00000000..36376e10
--- /dev/null
+++ b/Test/Fixtures/external_invoices/index-200.xml
@@ -0,0 +1,37 @@
+HTTP/1.1 200 OK
+Content-Type: application/xml; charset=utf-8
+
+<?xml version="1.0" encoding="UTF-8"?>
+<external_invoices type="array">
+    <external_invoice href="https://api.recurly.com/v2/external_invoices/twqswp6wgq68">
+        <account href="https://api.recurly.com/v2/accounts/fe337836-771f-4af8-b73f-0a8362f45197"/>
+        <external_subscription href="https://api.recurly.com/v2/external_subscriptions/tsfnx2vn5wh6"/>
+        <external_payment_phase href="https://api.recurly.com/v2/external_payment_phases/twqswp627ri3"/>
+        <external_id>2000000458276005</external_id>
+        <state>paid</state>
+        <currency>USD</currency>
+        <total>10.45</total>
+        <line_items type="array">
+            <external_charge>
+                <account href="https://api.recurly.com/v2/accounts/fe337836-771f-4af8-b73f-0a8362f45197"/>
+                <external_invoice href="https://api.recurly.com/v2/external_invoices/twqswp6wgq68"/>
+                <external_product_reference href="https://api.recurly.com/v2/external_product_references/twqswp9p3krc">
+                    <id>twqswp9p3krc</id>
+                    <reference_code>random-ass-test-2</reference_code>
+                    <external_connection_type>apple_app_store</external_connection_type>
+                    <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+                    <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+                </external_product_reference>
+                <description>the best banana in the world</description>
+                <unit_amount>10.45</unit_amount>
+                <currency>USD</currency>
+                <quantity>1</quantity>
+                <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+                <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+            </external_charge>
+        </line_items>
+        <purchased_at type="datetime">2023-11-14T14:15:22Z</purchased_at>
+        <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+        <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+    </external_invoice>
+</external_invoices>
\ No newline at end of file
diff --git a/Test/Fixtures/external_invoices/show-200.xml b/Test/Fixtures/external_invoices/show-200.xml
new file mode 100644
index 00000000..efb3a11f
--- /dev/null
+++ b/Test/Fixtures/external_invoices/show-200.xml
@@ -0,0 +1,35 @@
+HTTP/1.1 200 OK
+Content-Type: application/xml; charset=utf-8
+
+<?xml version="1.0" encoding="UTF-8"?>
+<external_invoice href="https://api.recurly.com/v2/external_invoices/twqswp6wgq68">
+    <account href="https://api.recurly.com/v2/accounts/fe337836-771f-4af8-b73f-0a8362f45197"/>
+    <external_subscription href="https://api.recurly.com/v2/external_subscriptions/tsfnx2vn5wh6"/>
+    <external_payment_phase href="https://api.recurly.com/v2/external_payment_phases/twqswp627ri3"/>
+    <external_id>2000000458276005</external_id>
+    <state>paid</state>
+    <currency>USD</currency>
+    <total>10.45</total>
+    <line_items type="array">
+        <external_charge>
+            <account href="https://api.recurly.com/v2/accounts/fe337836-771f-4af8-b73f-0a8362f45197"/>
+            <external_invoice href="https://api.recurly.com/v2/external_invoices/twqswp6wgq68"/>
+            <external_product_reference href="https://api.recurly.com/v2/external_product_references/twqswp9p3krc">
+                <id>twqswp9p3krc</id>
+                <reference_code>random-ass-test-2</reference_code>
+                <external_connection_type>apple_app_store</external_connection_type>
+                <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+                <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+            </external_product_reference>
+            <description>the best banana in the world</description>
+            <unit_amount>10.45</unit_amount>
+            <currency>USD</currency>
+            <quantity>1</quantity>
+            <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+            <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+        </external_charge>
+    </line_items>
+    <purchased_at type="datetime">2023-11-14T14:15:22Z</purchased_at>
+    <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+    <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+</external_invoice>
\ No newline at end of file
diff --git a/Test/Fixtures/external_payment_phases/index-200.xml b/Test/Fixtures/external_payment_phases/index-200.xml
new file mode 100644
index 00000000..e523bb94
--- /dev/null
+++ b/Test/Fixtures/external_payment_phases/index-200.xml
@@ -0,0 +1,21 @@
+HTTP/1.1 200 OK
+Content-Type: application/xml; charset=utf-8
+
+<?xml version="1.0" encoding="UTF-8"?>
+<external_payment_phases type="array">
+    <external_payment_phase href="https://api.recurly.com/v2/external_payment_phases/twqswp627ri3">
+        <id>twqswp627ri3</id>
+        <started_at type="datetime">2023-11-15T00:00:00Z</started_at>
+        <ends_at type="datetime">2023-11-17T21:27:10Z</ends_at>
+        <starting_billing_period_index>1</starting_billing_period_index>
+        <ending_billing_period_index>2</ending_billing_period_index>
+        <offer_type>FREE_TRIAL</offer_type>
+        <offer_name>introductory</offer_name>
+        <period_count>2</period_count>
+        <period_length>TWO WEEKS</period_length>
+        <amount>1.99</amount>
+        <currency>USD</currency>
+        <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+        <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+    </external_payment_phase>
+</external_payment_phases>
\ No newline at end of file
diff --git a/Test/Fixtures/external_payment_phases/show-200.xml b/Test/Fixtures/external_payment_phases/show-200.xml
new file mode 100644
index 00000000..281a08b0
--- /dev/null
+++ b/Test/Fixtures/external_payment_phases/show-200.xml
@@ -0,0 +1,19 @@
+HTTP/1.1 200 OK
+Content-Type: application/xml; charset=utf-8
+
+<?xml version="1.0" encoding="UTF-8"?>
+<external_payment_phase href="https://api.recurly.com/v2/external_payment_phases/twqswp627ri3">
+    <id>twqswp627ri3</id>
+    <started_at type="datetime">2023-11-15T00:00:00Z</started_at>
+    <ends_at type="datetime">2023-11-17T21:27:10Z</ends_at>
+    <starting_billing_period_index>1</starting_billing_period_index>
+    <ending_billing_period_index>2</ending_billing_period_index>
+    <offer_type>FREE_TRIAL</offer_type>
+    <offer_name>introductory</offer_name>
+    <period_count>2</period_count>
+    <period_length>TWO WEEKS</period_length>
+    <amount>1.99</amount>
+    <currency>USD</currency>
+    <created_at type="datetime">2023-11-15T16:16:43Z</created_at>
+    <updated_at type="datetime">2023-11-15T16:16:43Z</updated_at>
+</external_payment_phase>
\ No newline at end of file
diff --git a/Test/List/ExternalInvoiceListTest.cs b/Test/List/ExternalInvoiceListTest.cs
index 18abb8e2..787893cf 100644
--- a/Test/List/ExternalInvoiceListTest.cs
+++ b/Test/List/ExternalInvoiceListTest.cs
@@ -1,8 +1,7 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
+using System.Xml;
 using FluentAssertions;
-using Xunit;
+using Recurly.Test.Fixtures;
 
 namespace Recurly.Test
 {
@@ -11,8 +10,21 @@ public class ExternalInvoiceListTest : BaseTest
         [RecurlyFact(TestEnvironment.Type.Integration)]
         public void ListExternalInvoices()
         {
-            var externalInvoices = ExternalInvoices.List();
-            externalInvoices.Should().NotBeEmpty();
+            var xmlFixture = FixtureImporter.Get(FixtureType.ExternalInvoices, "index-200").Xml;
+            var externalInvoices = new ExternalInvoiceList();
+            XmlTextReader reader = new XmlTextReader(new System.IO.StringReader(xmlFixture));
+            externalInvoices.ReadXml(reader);
+            externalInvoices.Should().HaveCount(1);
+            var externalInvoice = externalInvoices[0];
+            externalInvoice.ExternalId.Should().Be("2000000458276005");
+            externalInvoice.State.Should().Be(ExternalInvoice.ExternalInvoiceState.Paid);
+            externalInvoice.Total.Should().Be(new decimal(10.45));
+            externalInvoice.Currency.Should().Be("USD");
+            externalInvoice.ExternalSubscriptionUuid.Should().Be("tsfnx2vn5wh6");
+            externalInvoice.ExternalPaymentPhaseUuid.Should().Be("twqswp627ri3");
+            externalInvoice.PurchasedAt.Should().NotBe(default(DateTime));
+            externalInvoice.CreatedAt.Should().NotBe(default(DateTime));
+            externalInvoice.UpdatedAt.Should().NotBe(default(DateTime));
         }
     }
 }
diff --git a/Test/List/ExternalPaymentPhaseListTest.cs b/Test/List/ExternalPaymentPhaseListTest.cs
new file mode 100644
index 00000000..28f7bdab
--- /dev/null
+++ b/Test/List/ExternalPaymentPhaseListTest.cs
@@ -0,0 +1,37 @@
+using System;
+
+using System.Xml;
+
+using FluentAssertions;
+
+using Recurly.Test.Fixtures;
+
+namespace Recurly.Test
+{
+    public class ExternalPaymentPhaseListTest : BaseTest
+    {
+        [RecurlyFact(TestEnvironment.Type.Integration)]
+        public void ListExternalPaymentPhase()
+        {
+            var xmlFixture = FixtureImporter.Get(FixtureType.ExternalPaymentPhases, "index-200").Xml;
+            var externalPaymentPhases = new ExternalPaymentPhaseList();
+            XmlTextReader reader = new XmlTextReader(new System.IO.StringReader(xmlFixture));
+            externalPaymentPhases.ReadXml(reader);
+            externalPaymentPhases.Should().HaveCount(1);
+            var externalPaymentPhase = externalPaymentPhases[0];
+            externalPaymentPhase.StartedAt.Should().Be(new DateTime(2023, 11, 15, 0, 0, 0, DateTimeKind.Utc));
+            externalPaymentPhase.EndsAt.Should().Be(new DateTime(2023, 11, 17, 21, 27, 10, DateTimeKind.Utc));
+            externalPaymentPhase.StartingBillingPeriodIndex.Should().Be(1);
+            externalPaymentPhase.EndingBillingPeriodIndex.Should().Be(2);
+            externalPaymentPhase.OfferType.Should().Be("FREE_TRIAL");
+            externalPaymentPhase.OfferName.Should().Be("introductory");
+            externalPaymentPhase.PeriodCount.Should().Be(2);
+            externalPaymentPhase.PeriodLength.Should().Be("TWO WEEKS");
+            externalPaymentPhase.Amount.Should().Be(new decimal(1.99));
+            externalPaymentPhase.Currency.Should().Be("USD");
+            externalPaymentPhase.CreatedAt.Should().Be(new DateTime(2023, 11, 15, 16, 16, 43, DateTimeKind.Utc));
+            externalPaymentPhase.UpdatedAt.Should().Be(new DateTime(2023, 11, 15, 16, 16, 43, DateTimeKind.Utc));
+
+        }
+    }
+}
diff --git a/Test/Recurly.Test.csproj b/Test/Recurly.Test.csproj
index 63f953e5..4fbb7ec8 100644
--- a/Test/Recurly.Test.csproj
+++ b/Test/Recurly.Test.csproj
@@ -206,6 +206,18 @@
     <Content Include="Fixtures\transactions\show-200.xml">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>
+    <Content Include="Fixtures/external_payment_phases/index-200.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+    <Content Include="Fixtures/external_payment_phases/show-200.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+    <Content Include="Fixtures/external_invoices/index-200.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+    <Content Include="Fixtures/external_invoices/show-200.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
   </ItemGroup>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it.
        Other similar extension points exist, see Microsoft.Common.targets.