diff --git a/.gitmodules b/.gitmodules
index 63fa691..4531d43 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -16,3 +16,6 @@
 [submodule "Nerfed.Runtime/Libraries/ImGui.NET"]
 	path = Nerfed.Runtime/Libraries/ImGui.NET
 	url = https://github.com/ImGuiNET/ImGui.NET.git
+[submodule "Nerfed.Runtime/Libraries/ECS"]
+	path = Nerfed.Runtime/Libraries/ECS
+	url = https://github.com/MoonsideGames/MoonTools.ECS.git
diff --git a/Nerfed.Editor/Program.cs b/Nerfed.Editor/Program.cs
index 6b21d4a..28f6de0 100644
--- a/Nerfed.Editor/Program.cs
+++ b/Nerfed.Editor/Program.cs
@@ -1,9 +1,15 @@
-using Nerfed.Runtime;
+using MoonTools.ECS;
+using Nerfed.Runtime;
+using Nerfed.Runtime.Systems;
+using System.Numerics;
 
 namespace Nerfed.Editor;
 
 internal class Program
 {
+    private static readonly World world = new World();
+    private static List<MoonTools.ECS.System> systems = new List<MoonTools.ECS.System>();
+
     private static void Main(string[] args)
     {
         Engine.OnInitialize += HandleOnInitialize;
@@ -16,6 +22,16 @@ private static void Main(string[] args)
 
     private static void HandleOnInitialize()
     {
+        systems.Add(new ParentSystem(world));
+        systems.Add(new TransformSystem(world));
+
+        Entity ent1 = world.CreateEntity();
+        world.Set(ent1, new LocalTransform(new Vector3(1, 0, 0), Quaternion.Identity, Vector3.One));
+
+        Entity ent2 = world.CreateEntity();
+        world.Set(ent2, new LocalTransform(new Vector3(0, 1, 0), Quaternion.Identity, Vector3.One));
+        world.Set(ent2, new Parent(ent1));
+
         // Open project.
         // Setip EditorGui.
         EditorGui.Initialize();
@@ -23,6 +39,11 @@ private static void HandleOnInitialize()
 
     private static void HandleOnUpdate()
     {
+        foreach (MoonTools.ECS.System system in systems)
+        {
+            system.Update(Engine.Timestep);
+        }
+
         // Editor Update.
         EditorGui.Update();
 
diff --git a/Nerfed.Runtime/Components/LocalToWorld.cs b/Nerfed.Runtime/Components/LocalToWorld.cs
new file mode 100644
index 0000000..a3f3fea
--- /dev/null
+++ b/Nerfed.Runtime/Components/LocalToWorld.cs
@@ -0,0 +1,6 @@
+using System.Numerics;
+
+namespace Nerfed.Runtime.Components
+{
+    public readonly record struct LocalToWorld(Matrix4x4 localToWorldMatrix);
+}
\ No newline at end of file
diff --git a/Nerfed.Runtime/Components/LocalTransform.cs b/Nerfed.Runtime/Components/LocalTransform.cs
new file mode 100644
index 0000000..f686c50
--- /dev/null
+++ b/Nerfed.Runtime/Components/LocalTransform.cs
@@ -0,0 +1,18 @@
+using System.Numerics;
+
+namespace Nerfed.Runtime.Components
+{
+    public struct LocalTransform
+    {
+        public Vector3 position;
+        public Quaternion rotation;
+        public Vector3 scale;
+
+        public LocalTransform(Vector3 position, Quaternion rotation, Vector3 scale)
+        {
+            this.position = position;
+            this.rotation = rotation;
+            this.scale = scale;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Nerfed.Runtime/Components/Parent.cs b/Nerfed.Runtime/Components/Parent.cs
new file mode 100644
index 0000000..bc65061
--- /dev/null
+++ b/Nerfed.Runtime/Components/Parent.cs
@@ -0,0 +1,8 @@
+using MoonTools.ECS;
+
+namespace Nerfed.Runtime.Components
+{
+    public readonly record struct Parent(Entity parentEntity);
+    public readonly record struct PreviousParent(Entity parentEntity);
+    public readonly record struct ChildRelation;
+}
\ No newline at end of file
diff --git a/Nerfed.Runtime/Libraries/ECS b/Nerfed.Runtime/Libraries/ECS
new file mode 160000
index 0000000..76b18a6
--- /dev/null
+++ b/Nerfed.Runtime/Libraries/ECS
@@ -0,0 +1 @@
+Subproject commit 76b18a6ba9a33f5a93022390be7ed805f9f722e8
diff --git a/Nerfed.Runtime/Nerfed.Runtime.csproj b/Nerfed.Runtime/Nerfed.Runtime.csproj
index 01615fb..f493dad 100644
--- a/Nerfed.Runtime/Nerfed.Runtime.csproj
+++ b/Nerfed.Runtime/Nerfed.Runtime.csproj
@@ -32,12 +32,13 @@
     </PropertyGroup>
     
     <ItemGroup>
-        <Compile Include="Libraries\SDL2CS\src\SDL2.cs"/>
-        <Compile Include="Libraries\RefreshCS\RefreshCS.cs"/>
-        <Compile Include="Libraries\FAudio\csharp\FAudio.cs"/>
-        <Compile Include="Libraries\WellspringCS\WellspringCS.cs"/>
-        <Compile Include="Libraries\dav1dfile\csharp\dav1dfile.cs"/>
-        <Compile Include="Libraries\ImGui.NET\src\ImGui.NET\**\*.cs"/>
+		<Compile Include="Libraries\ECS\src\**\*.cs" />
+		<Compile Include="Libraries\SDL2CS\src\SDL2.cs" />
+        <Compile Include="Libraries\RefreshCS\RefreshCS.cs" />
+        <Compile Include="Libraries\FAudio\csharp\FAudio.cs" />
+        <Compile Include="Libraries\WellspringCS\WellspringCS.cs" />
+        <Compile Include="Libraries\dav1dfile\csharp\dav1dfile.cs" />
+        <Compile Include="Libraries\ImGui.NET\src\ImGui.NET\**\*.cs" />
     </ItemGroup>
     
 </Project>
\ No newline at end of file
diff --git a/Nerfed.Runtime/Systems/ParentSystem.cs b/Nerfed.Runtime/Systems/ParentSystem.cs
new file mode 100644
index 0000000..0aed0ad
--- /dev/null
+++ b/Nerfed.Runtime/Systems/ParentSystem.cs
@@ -0,0 +1,62 @@
+using MoonTools.ECS;
+using Nerfed.Runtime.Components;
+
+namespace Nerfed.Runtime.Systems
+{
+    public class ParentSystem : MoonTools.ECS.System
+    {
+        private readonly Filter parentsAddedFilter;
+        private readonly Filter parentsRemovedFilter;
+        private readonly Filter parentsFilter;
+
+        public ParentSystem(World world) : base(world)
+        {
+            parentsAddedFilter = FilterBuilder.Include<Parent>().Exclude<PreviousParent>().Build();
+            parentsRemovedFilter = FilterBuilder.Include<PreviousParent>().Exclude<Parent>().Build();
+            parentsFilter = FilterBuilder.Include<Parent>().Include<PreviousParent>().Build();
+        }
+
+        public override void Update(TimeSpan delta)
+        {
+            // Update removed parents.
+            foreach (Entity entity in parentsRemovedFilter.Entities)
+            {
+                // Do stuff here to update/remove child relations etc.
+                PreviousParent previousParent = Get<PreviousParent>(entity);
+                World.Unrelate<ChildRelation>(previousParent.parentEntity, entity);
+                Remove<PreviousParent>(entity);
+            }
+
+            // Update added parents.
+            foreach (Entity entity in parentsAddedFilter.Entities)
+            {
+                Parent parent = Get<Parent>(entity);
+
+                if (Has<Parent>(parent.parentEntity) && Get<Parent>(parent.parentEntity).parentEntity == entity)
+                {
+                    Log.Warning($"Entity {entity} cannot be a parent of entity {parent.parentEntity}, because {parent.parentEntity} is the parent of {entity}");
+                    Remove<Parent>(entity);
+                    continue;
+                }
+
+                PreviousParent previousParent = new(parent.parentEntity);
+                Set(entity, previousParent);
+                World.Relate(parent.parentEntity, entity, new ChildRelation());
+            }
+
+            // Update relations if the parent has changed.
+            foreach (Entity entity in parentsFilter.Entities)
+            {
+                Parent parent = Get<Parent>(entity);
+                PreviousParent previousParent = Get<PreviousParent>(entity);
+
+                if(parent.parentEntity != previousParent.parentEntity)
+                {
+                    World.Unrelate<ChildRelation>(previousParent.parentEntity, entity);
+                    Set(entity, new PreviousParent(parent.parentEntity));
+                    World.Relate(parent.parentEntity, entity, new ChildRelation());
+                }
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Nerfed.Runtime/Systems/TransformSystem.cs b/Nerfed.Runtime/Systems/TransformSystem.cs
new file mode 100644
index 0000000..4d5fc8b
--- /dev/null
+++ b/Nerfed.Runtime/Systems/TransformSystem.cs
@@ -0,0 +1,47 @@
+using MoonTools.ECS;
+using Nerfed.Runtime.Components;
+using Nerfed.Runtime.Util;
+using System.Numerics;
+
+namespace Nerfed.Runtime.Systems
+{
+    public class TransformSystem : MoonTools.ECS.System
+    {
+        private readonly Filter rootEntitiesFilter;
+
+        public TransformSystem(World world) : base(world)
+        {
+            rootEntitiesFilter = FilterBuilder.Include<LocalTransform>().Exclude<Parent>().Build();
+        }
+
+        public override void Update(TimeSpan delta)
+        {
+            Matrix4x4 rootMatrix = Matrix4x4.Identity;
+
+            foreach (Entity entity in rootEntitiesFilter.Entities)
+            {
+                UpdateWorldTransform(entity, rootMatrix);
+            }
+        }
+
+        private void UpdateWorldTransform(in Entity entity, in Matrix4x4 parentLocalToWorld)
+        {
+            // TODO: Only update dirty transforms.
+            // Maybe store the local transform matrix.
+            // If something is dirty all the children need to update their localToWorld matrix.
+
+            LocalTransform localTransform = Get<LocalTransform>(entity);
+            Matrix4x4 localToWorldMatrix = Matrix4x4.Multiply(parentLocalToWorld, localTransform.TRS());
+            LocalToWorld localToWorld = new(localToWorldMatrix);
+            Set(entity, localToWorld);
+
+            Log.Info($"Entity {entity} | local position {localTransform.position} | world position {localToWorldMatrix.Translation}");
+
+            ReverseSpanEnumerator<Entity> childEntities = World.OutRelations<ChildRelation>(entity);
+            foreach (Entity childEntity in childEntities)
+            {
+                UpdateWorldTransform(childEntity, localToWorldMatrix);
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Nerfed.Runtime/Util/Transform.cs b/Nerfed.Runtime/Util/Transform.cs
new file mode 100644
index 0000000..6885538
--- /dev/null
+++ b/Nerfed.Runtime/Util/Transform.cs
@@ -0,0 +1,25 @@
+using Nerfed.Runtime.Components;
+using System.Numerics;
+
+namespace Nerfed.Runtime.Util
+{
+    // https://github.com/needle-mirror/com.unity.entities/blob/master/Unity.Transforms/TransformHelpers.cs
+    internal static class Transform
+    {
+        public static Vector3 Forward(in this Matrix4x4 matrix) => new Vector3(matrix.M31, matrix.M32, matrix.M33);
+        public static Vector3 Back(in this Matrix4x4 matrix) => -matrix.Forward();
+        public static Vector3 Up(in this Matrix4x4 matrix) => new Vector3(matrix.M21, matrix.M22, matrix.M23);
+        public static Vector3 Down(in this Matrix4x4 matrix) => -matrix.Up();
+        public static Vector3 Right(in this Matrix4x4 matrix) => new Vector3(matrix.M11, matrix.M12, matrix.M13);
+        public static Vector3 Left(in this Matrix4x4 matrix) => -matrix.Right();
+        //public static Vector3 Translation(in this Matrix4x4 matrix) => new Vector3();
+        //public static Quaternion Rotation(in this Matrix4x4 matrix) => new Quaternion();
+
+        public static Matrix4x4 TRS(in this LocalTransform localTransform)
+        {
+            return Matrix4x4.CreateScale(localTransform.scale) *
+                Matrix4x4.CreateFromQuaternion(localTransform.rotation) *
+                Matrix4x4.CreateTranslation(localTransform.position);
+        }
+    }
+}
\ No newline at end of file