1. Introduction; 2. What is agreement?; 3. Domains of agreement and categories involved; 4. Problems with agreement; 5. Grammatical, ambiguous and anaphoric agreement; 6. Marginal agreement; 7. The sample of languages; 8. Areal and genetic patterns in agreement systems; 9. Typological correlations in agreement systems; 10. Diachronic patterns in the development of agreement; 11. Conclusions.