Cohomology of arithmetic groups serves as a tool in studying possible relations between the theory of automorphic forms and the arithmetic of algebraic varieties respecting 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. This book of proceedings on automorphic forms, number theory, arithmetic algebraic geometry, discrete subgroups of lie groups and representation theory is intended for researchers and graduate students in the above fields.