diff --git a/Shared/IWorld.cs b/Shared/IWorld.cs
new file mode 100644
index 0000000..9776d06
--- /dev/null
+++ b/Shared/IWorld.cs
@@ -0,0 +1,8 @@
+using System;
+
+namespace SemiColinGames {
+  public interface IWorld : IDisposable {
+    void Update(float modelTime, History<Input> input);
+    Camera Camera { get; }
+  }
+}
diff --git a/Shared/Scene.cs b/Shared/Scene.cs
index 4e929f7..39fec6c 100644
--- a/Shared/Scene.cs
+++ b/Shared/Scene.cs
@@ -56,7 +56,8 @@ namespace SemiColinGames {
       GC.SuppressFinalize(this);
     }
 
-    public void Draw(bool isRunningSlowly, World world, bool paused) {
+    public void Draw(bool isRunningSlowly, IWorld iworld, bool paused) {
+      World world = (World) iworld;
       graphics.SetRenderTarget(null);
       graphics.Clear(backgroundColor);
 
diff --git a/Shared/Shared.projitems b/Shared/Shared.projitems
index 7e6c612..591a9ce 100644
--- a/Shared/Shared.projitems
+++ b/Shared/Shared.projitems
@@ -12,6 +12,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Camera.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ExtensionMethods.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)FSM.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)IWorld.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)NPC.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ProfilingList.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SoundEffects.cs" />
diff --git a/Shared/SneakGame.cs b/Shared/SneakGame.cs
index f3dc04a..c6b5b3d 100644
--- a/Shared/SneakGame.cs
+++ b/Shared/SneakGame.cs
@@ -22,7 +22,7 @@ namespace SemiColinGames {
     readonly Timer drawTimer = new Timer(TARGET_FRAME_TIME / 2.0, "DrawTimer");
 
     Scene scene;
-    World world;
+    IWorld world;
 
     public SneakGame() {
       Debug.WriteLine("MonoGame platform: " + PlatformInfo.MonoGamePlatform +
diff --git a/Shared/World.cs b/Shared/World.cs
index e52fc2e..e1bb2f5 100644
--- a/Shared/World.cs
+++ b/Shared/World.cs
@@ -6,7 +6,7 @@ using System.Collections.Generic;
 
 namespace SemiColinGames {
 
-  public sealed class World : IDisposable {
+  public sealed class World : IWorld {
 
     // Size of World in terms of tile grid.
     private int gridWidth;