diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..5951351
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "book/external/Nested-Books"]
+	path = book/external/Nested-Books
+	url = git@github.com:TeachBooks/Nested-Books.git
diff --git a/book/external/Nested-Books b/book/external/Nested-Books
new file mode 160000
index 0000000..8ea5a17
--- /dev/null
+++ b/book/external/Nested-Books
@@ -0,0 +1 @@
+Subproject commit 8ea5a179daab16358ebcf1620638479fe5fdeea1