diff --git a/.gitignore b/.gitignore
index af968b2..d060c06 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,7 +18,11 @@ packages/
 Thumbs.db
 
 # Reference repos and retail client (large, not our code, separate licenses)
-references/
+# WorldBuilder is exempt — it's a load-bearing dependency tracked as a git
+# submodule pointing at our fork (Phase N, see docs/architecture/worldbuilder-inventory.md).
+references/*
+!references/WorldBuilder
+!references/WorldBuilder/
 
 # Claude Code session state
 .claude/
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..c691aa8
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,4 @@
+[submodule "references/WorldBuilder"]
+	path = references/WorldBuilder
+	url = git@github.com:eriknihlen/WorldBuilder.git
+	branch = acdream
diff --git a/references/WorldBuilder b/references/WorldBuilder
new file mode 160000
index 0000000..167788b
--- /dev/null
+++ b/references/WorldBuilder
@@ -0,0 +1 @@
+Subproject commit 167788be6fce65f5ebe79eef07a0b7d28bd7aa81
diff --git a/src/AcDream.Core/AcDream.Core.csproj b/src/AcDream.Core/AcDream.Core.csproj
index 6155c02..1ac800c 100644
--- a/src/AcDream.Core/AcDream.Core.csproj
+++ b/src/AcDream.Core/AcDream.Core.csproj
@@ -18,5 +18,13 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\AcDream.Plugin.Abstractions\AcDream.Plugin.Abstractions.csproj" />
+    <!-- Phase N: WorldBuilder is acdream's rendering + dat-handling base.
+         See docs/architecture/worldbuilder-inventory.md for the inventory of
+         what we use from WB vs port from retail decomp ourselves.
+         WorldBuilder.Shared = stateless helpers (TerrainUtils, TerrainEntry, RegionInfo).
+         Chorizite.OpenGLSDLBackend = render managers + SceneryHelpers + ParticleEmitterRenderer
+         (full GL pipeline; we currently use only the stateless SceneryHelpers from it). -->
+    <ProjectReference Include="..\..\references\WorldBuilder\WorldBuilder.Shared\WorldBuilder.Shared.csproj" />
+    <ProjectReference Include="..\..\references\WorldBuilder\Chorizite.OpenGLSDLBackend\Chorizite.OpenGLSDLBackend.csproj" />
   </ItemGroup>
 </Project>