diff --git a/_toc.yml b/_toc.yml
index 1c59189..ed3b58b 100644
--- a/_toc.yml
+++ b/_toc.yml
@@ -1,46 +1,63 @@
 # PBDL Table of content (cf https://jupyterbook.org/customize/toc.html)
 #
+
 - file: intro.md
-  sections:
-    - file: intro-teaser.ipynb
-- file: overview.md
-  sections:
-    - file: overview-equations.md
-    - file: overview-burgers-forw.ipynb
-    - file: overview-ns-forw.ipynb
-- file: supervised.md
-  sections:
-    - file: supervised-airfoils.ipynb
-    - file: supervised-discuss.md
-- file: physicalloss.md
-  sections:
-    - file: physicalloss-code.ipynb
-    - file: physicalloss-discuss.md
-- file: diffphys.md
-  sections:
-    - file: diffphys-code-burgers.ipynb
-    - file: diffphys-discuss.md
-    - file: diffphys-code-ns.ipynb
-    - file: diffphys-dpvspinn.md
-- file: diffphys-examples.md
-  sections:
-    - file: diffphys-code-sol.ipynb
-    - file: diffphys-control.ipynb
-    - file: diffphys-outlook.md
-- file: physgrad.md
-  sections:
-    - file: physgrad-comparison.ipynb
-    - file: physgrad-nn.md
-    - file: physgrad-discuss.md
-- file: outlook.md
-- file: old-phiflow1.md
-  sections:
-    - file: overview-burgers-forw-v1.ipynb
-    - file: overview-ns-forw-v1.ipynb
-    - file: physicalloss-code-v2.ipynb
-    - file: diffphys-code-gradient-v1.ipynb
-    - file: diffphys-code-tf.ipynb
-    - file: diffphys-code-ns-v1.ipynb
-    - file: diffphys-code-ns-v2a.ipynb
-- file: references.md
-- file: notation.md
+
+- part: Introduction
+  chapters:
+  - file: intro-teaser.ipynb
+  - file: overview.md
+    sections:
+      - file: overview-equations.md
+      - file: overview-burgers-forw.ipynb
+      - file: overview-ns-forw.ipynb
+  - file: supervised.md
+    sections:
+      - file: supervised-airfoils.ipynb
+      - file: supervised-discuss.md
+
+- part: Physical Losses
+  chapters:
+  - file: physicalloss.md
+  - file: physicalloss-code.ipynb
+  - file: physicalloss-discuss.md
+
+- part: Differentiable Physics
+  chapters:
+  - file: diffphys.md
+    sections:
+      - file: diffphys-code-burgers.ipynb
+      - file: diffphys-discuss.md
+      - file: diffphys-code-ns.ipynb
+      - file: diffphys-dpvspinn.md
+  - file: diffphys-examples.md
+    sections:
+      - file: diffphys-code-sol.ipynb
+      - file: diffphys-control.ipynb
+      - file: diffphys-outlook.md
+
+- part: Physical Gradients
+  chapters:
+  - file: physgrad.md
+    sections:
+      - file: physgrad-comparison.ipynb
+      - file: physgrad-nn.md
+      - file: physgrad-discuss.md
+  
+- part: End Matter
+  chapters:
+  - file: outlook.md
+  - file: old-phiflow1.md
+    sections:
+      - file: overview-burgers-forw-v1.ipynb
+      - file: overview-ns-forw-v1.ipynb
+      - file: physicalloss-code-v2.ipynb
+      - file: diffphys-code-gradient-v1.ipynb
+      - file: diffphys-code-tf.ipynb
+      - file: diffphys-code-ns-v1.ipynb
+      - file: diffphys-code-ns-v2a.ipynb
+  - file: references.md
+  - file: notation.md
+  
+  
+