Organized in chronological order, this volume brings together the major contributions of J.L. Koszul and some expository articles. The main subjects included are: cohomology of Lie algebras; relative cohomology; reductive subalgebras and transgression theorem; the formalim of spectral sequences; Koszul complexes ; proper and differentiable actions of Lie groups; slices; hermitian forms on complex homogeneous domains; bounded domains; locally flat manifolds; convex homogeneous domains; simplicial spaces; themes related to Gelfand Fuks theory and supergeometry.