diff --git a/src/ThreeDModels/Format/Gltf/Extensions/CESIUM_primitive_outline.cs b/src/ThreeDModels/Format/Gltf/Extensions/CESIUM_primitive_outline.cs
new file mode 100644
index 0000000..4a3ac1d
--- /dev/null
+++ b/src/ThreeDModels/Format/Gltf/Extensions/CESIUM_primitive_outline.cs
@@ -0,0 +1,73 @@
+using System.Text.Json;
+using ThreeDModels.Format.Gltf.Elements;
+using ThreeDModels.Format.Gltf.IO;
+using static ThreeDModels.Format.Gltf.IO.Utf8JsonReaderHelpers;
+
+namespace ThreeDModels.Format.Gltf.Extensions;
+
+/// <summary>
+/// Represents an object that indicates that some edges of a primitive's triangles should be outlined.
+/// </summary>
+public class CESIUM_primitive_outline : IGltfProperty
+{
+    public int? Indices { get; set; }
+    public Dictionary<string, object?>? Extensions { get; set; }
+    public object? Extras { get; set; }
+}
+
+public class CesiumPrimitiveOutlineExtension : IGltfExtension
+{
+    public string Name => nameof(CESIUM_primitive_outline);
+
+    public object? Read(ref Utf8JsonReader jsonReader, GltfReaderContext context, Type parentType)
+    {
+        if (parentType != typeof(MeshPrimitive))
+        {
+            throw new InvalidDataException("CESIUM_primitive_outline must be used in a MeshPrimitive.");
+        }
+        int? indices = null;
+        Dictionary<string, object?>? extensions = null;
+        object? extras = null;
+        if (jsonReader.TokenType == JsonTokenType.PropertyName && jsonReader.Read())
+        {
+        }
+        if (jsonReader.TokenType == JsonTokenType.Null)
+        {
+            return null;
+        }
+        else if (jsonReader.TokenType != JsonTokenType.StartObject)
+        {
+            throw new InvalidDataException("Failed to find start of property.");
+        }
+        while (jsonReader.Read())
+        {
+            if (jsonReader.TokenType == JsonTokenType.EndObject)
+            {
+                break;
+            }
+            var propertyName = jsonReader.GetString();
+            if (propertyName == nameof(indices))
+            {
+                indices = ReadInteger(ref jsonReader);
+            }
+            else if (propertyName == nameof(extensions))
+            {
+                extensions = ExtensionsSerialization.Read<CESIUM_primitive_outline>(ref jsonReader, context);
+            }
+            else if (propertyName == nameof(extras))
+            {
+                extras = JsonSerialization.Read(ref jsonReader, context);
+            }
+            else
+            {
+                throw new InvalidDataException($"Unknown property: {propertyName}");
+            }
+        }
+        return new CESIUM_primitive_outline()
+        {
+            Indices = indices,
+            Extensions = extensions,
+            Extras = extras,
+        };
+    }
+}