diff --git a/book.toml b/book.toml
index 85f443a..c46f4e8 100644
--- a/book.toml
+++ b/book.toml
@@ -21,5 +21,14 @@ git-repository-url = "https://github.com/rust-lang/nomicon"
 "/vec-zsts.html" = "/vec/vec-zsts.html"
 "/vec.html" = "/vec/vec.html"
 
+# Arc and Mutex related chapters.
+"/arc-and-mutex.html" = "/arc-mutex/arc-and-mutex.html"
+"/arc-base.html" = "/arc-mutex/arc-base.html"
+"/arc-clone.html" = "/arc-mutex/arc-clone.html"
+"/arc-drop.html" = "/arc-mutex/arc-drop.html"
+"/arc-final.html" = "/arc-mutex/arc-final.html"
+"/arc-layout.html" = "/arc-mutex/arc-layout.html"
+"/arc.html" = "/arc-mutex/arc.html"
+
 [rust]
 edition = "2018"
diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 34b1405..84223ed 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -54,13 +54,13 @@
   * [Drain](./vec/vec-drain.md)
   * [Handling Zero-Sized Types](./vec/vec-zsts.md)
   * [Final Code](./vec/vec-final.md)
-* [Implementing Arc and Mutex](arc-and-mutex.md)
-  * [Arc](arc.md)
-    * [Layout](arc-layout.md)
-    * [Base Code](arc-base.md)
-    * [Cloning](arc-clone.md)
-    * [Dropping](arc-drop.md)
-    * [Final Code](arc-final.md)
+* [Implementing Arc and Mutex](./arc-mutex/arc-and-mutex.md)
+  * [Arc](./arc-mutex/arc.md)
+    * [Layout](./arc-mutex/arc-layout.md)
+    * [Base Code](./arc-mutex/arc-base.md)
+    * [Cloning](./arc-mutex/arc-clone.md)
+    * [Dropping](./arc-mutex/arc-drop.md)
+    * [Final Code](./arc-mutex/arc-final.md)
 * [FFI](ffi.md)
 * [Beneath `std`](beneath-std.md)
   * [#[panic_handler]](panic-handler.md)
diff --git a/src/arc-and-mutex.md b/src/arc-mutex/arc-and-mutex.md
similarity index 62%
rename from src/arc-and-mutex.md
rename to src/arc-mutex/arc-and-mutex.md
index f6c1583..41a4d7c 100644
--- a/src/arc-and-mutex.md
+++ b/src/arc-mutex/arc-and-mutex.md
@@ -2,6 +2,6 @@
 
 Knowing the theory is all fine and good, but the *best* way to understand
 something is to use it. To better understand atomics and interior mutability,
-we'll be implementing versions of the standard library's Arc and Mutex types.
+we'll be implementing versions of the standard library's `Arc` and `Mutex` types.
 
-TODO: Mutex
+TODO: Write `Mutex` chapters.
diff --git a/src/arc-base.md b/src/arc-mutex/arc-base.md
similarity index 100%
rename from src/arc-base.md
rename to src/arc-mutex/arc-base.md
diff --git a/src/arc-clone.md b/src/arc-mutex/arc-clone.md
similarity index 100%
rename from src/arc-clone.md
rename to src/arc-mutex/arc-clone.md
diff --git a/src/arc-drop.md b/src/arc-mutex/arc-drop.md
similarity index 100%
rename from src/arc-drop.md
rename to src/arc-mutex/arc-drop.md
diff --git a/src/arc-final.md b/src/arc-mutex/arc-final.md
similarity index 100%
rename from src/arc-final.md
rename to src/arc-mutex/arc-final.md
diff --git a/src/arc-layout.md b/src/arc-mutex/arc-layout.md
similarity index 100%
rename from src/arc-layout.md
rename to src/arc-mutex/arc-layout.md
diff --git a/src/arc.md b/src/arc-mutex/arc.md
similarity index 100%
rename from src/arc.md
rename to src/arc-mutex/arc.md