Preface, 1. Preliminaries, 2. Algebraic Structures, 3. Automata and Languages, 4. Syntactic Monoids of Automata, 5. Congruences on Automata, 6. Minimal Automata, 7. Languages, 8. Tree Languages, 9. Equational Theories, 10. Groupoid Rings, 11. Dualities, Topologies, Flatness, 12. Open Problems, Appendix A. Glossary of Notation, Bibliography, Index