Introduction; Part I. Toposes and Differential Geometry: 1. Topos theory; 2. Synthetic differential geometry; Part II. Topics in SDG: 3. The Ambrose–Palais–Singer theorem in SDG; 4. Calculus of variations in SDG; Part III. Toposes and Differential Topology: 5. Local concepts in SDG; 6. Synthetic differential topology; Part IV. Topics in SDT: 7. Stable mappings and Mather's theorem in SDT; 8. Morse theory in SDT; Part V. SDT and Differential Topology: 9. Well-adapted models of SDT; 10. An application to unfoldings; Part VI. A Well-Adapted Model of SDT: 11. The Dubuc topos G; 12. G as a model of SDT; References; Index.