diff --git a/src/Resend/Contact.cs b/src/Resend/Contact.cs
index 768297e..a2d3f9f 100644
--- a/src/Resend/Contact.cs
+++ b/src/Resend/Contact.cs
@@ -52,5 +52,5 @@ public class Contact
     /// </summary>
     [JsonPropertyName( "properties" )]
     [JsonIgnore( Condition = JsonIgnoreCondition.WhenWritingNull )]
-    public Dictionary<string,string>? Properties { get; set; }
+    public Dictionary<string, ContactPropertyValue>? Properties { get; set; }
 }
\ No newline at end of file
diff --git a/src/Resend/ContactPropertyType.cs b/src/Resend/ContactPropertyType.cs
index 8bef41b..e43b9bc 100644
--- a/src/Resend/ContactPropertyType.cs
+++ b/src/Resend/ContactPropertyType.cs
@@ -19,4 +19,10 @@ public enum ContactPropertyType
     /// </summary>
     [JsonStringValue( "number" )]
     Number,
+
+    /// <summary>
+    /// Boolean.
+    /// </summary>
+    [JsonStringValue( "boolean" )]
+    Boolean,
 }
\ No newline at end of file
diff --git a/src/Resend/ContactPropertyValue.cs b/src/Resend/ContactPropertyValue.cs
new file mode 100644
index 0000000..e5410ed
--- /dev/null
+++ b/src/Resend/ContactPropertyValue.cs
@@ -0,0 +1,22 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Resend;
+
+/// <summary>
+/// Custom property value on a contact.
+/// </summary>
+public class ContactPropertyValue
+{
+    /// <summary>
+    /// Property value; a string, number, or boolean, depending on <see cref="PropertyType"/>.
+    /// </summary>
+    [JsonPropertyName( "value" )]
+    public JsonElement Value { get; set; }
+
+    /// <summary>
+    /// Property data-type.
+    /// </summary>
+    [JsonPropertyName( "type" )]
+    public ContactPropertyType PropertyType { get; set; }
+}
diff --git a/tests/Resend.Tests/ResendClientTests.cs b/tests/Resend.Tests/ResendClientTests.cs
index 7bcd9ca..5afebd7 100644
--- a/tests/Resend.Tests/ResendClientTests.cs
+++ b/tests/Resend.Tests/ResendClientTests.cs
@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Mvc.Testing;
 using Resend.ApiServer;
 using System.Net;
+using System.Text.Json;
 
 namespace Resend.Tests;
 
@@ -328,6 +329,11 @@ public async Task ContactRetrieve()
         var resp = await _resend.ContactRetrieveAsync( Guid.NewGuid() );
 
         Assert.NotNull( resp );
+        Assert.NotNull( resp.Content.Properties );
+
+        var tier = resp.Content.Properties[ "tier" ];
+        Assert.Equal( ContactPropertyType.String, tier.PropertyType );
+        Assert.Equal( "premium", tier.Value.GetString() );
     }
 
 
diff --git a/tools/Resend.ApiServer/Controllers/ContactController.cs b/tools/Resend.ApiServer/Controllers/ContactController.cs
index 0d984d3..b5e5e13 100644
--- a/tools/Resend.ApiServer/Controllers/ContactController.cs
+++ b/tools/Resend.ApiServer/Controllers/ContactController.cs
@@ -1,5 +1,6 @@
 using Microsoft.AspNetCore.Mvc;
 using Resend.Payloads;
+using System.Text.Json;
 
 namespace Resend.ApiServer.Controllers;
 
@@ -47,6 +48,10 @@ public Contact ContactRetrieve( [FromRoute] Guid contactId )
             LastName = "Test",
             MomentCreated = DateTime.UtcNow.AddDays( -1 ),
             IsUnsubscribed = true,
+            Properties = new Dictionary<string, ContactPropertyValue>()
+            {
+                { "tier", new ContactPropertyValue() { Value = JsonDocument.Parse( "\"premium\"" ).RootElement, PropertyType = ContactPropertyType.String } },
+            },
         };
     }