Complexes.- Coxeter complexes.- Buildings.- Reduction.- The building of a semi-simple algebraic group.- Buildings of type An, Dn, En.- Buildings of type Cn. I. Polar spaces.- Buildings of type Cn. II. Projective embeddings of polar spaces.- Buildings of type Cn. III. Non-embeddable polar spaces.- Buildings of type F4.- Finite BN-pairs of irreducible type and rank ? 3.- Appendix 1. Shadows.- Appendix 2. Generators and relations.