The notes in this volume were written as a part of a Nachdiplom course
that I gave at the ETH in the summer semester of 1995. The aim of my
lectures was the development of some of the basics of the interaction of
homological algebra, or more specifically the cohomology of groups, and
modular representation theory. Every time that I had given such a course
in the past fifteen years, the choice of the material and the order of
presentation of the results have followed more or less the same basic
pattern. Such a course began with the fundamentals of group cohomology,
and then investigated the structure of cohomology rings, and their
maximal ideal spectra. Then the variety of a module was defined and
related to actual module structure through the rank variety.
Applications followed. The standard approach was used in my University
of Essen Lecture Notes [e1] in 1984. Evens [E] and Benson [B2]
have written it up in much clearer detail and included it as part of
their books on the subject.