diff --git a/source/index.rst b/source/index.rst
index a9f0728..12f02a9 100644
--- a/source/index.rst
+++ b/source/index.rst
@@ -49,6 +49,12 @@ Welcome to ScienceNotes's documentation!
    calculus/notations.rst
    calculus/ode.rst
 
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+   :caption: Machine Learning
+
+   ml/nn.rst
 
 Indices and tables
 ==================
diff --git a/source/ml/nn.rst b/source/ml/nn.rst
new file mode 100644
index 0000000..14022ad
--- /dev/null
+++ b/source/ml/nn.rst
@@ -0,0 +1,6 @@
+Neural Networks
+================================
+
+todo
+
+