Preface; 1. Locally integrable structures; 2. The Baouendi-Treves approximation formula; 3. Sussmann’s orbits and unique continuation; 4. Local solvability of vector fields; 5. The FBI transform and some applications; 6. Some boundary properties of solutions; 7. The differential complex associated to a formally integrable structure; 8. Local solvability in locally integrable structures; Epilogue; Bibliography; A. Hardy space lemmas.