Cohomology of Arithmetic Groups and Automorphic Forms : Proceedings of a Conference held in Luminy Marseille France May 22–27 1989 Cohomology of arithmetic groups serves as a tool in studying possible relations between the theory of automorphic forms and the arithmetic of algebraic varieties resp. the geometry of locally symmetric spaces. These proceedings will serve as a guide to this still rapidly developing area of mathematics. Besides two survey articles the contributions are original research papers