The aim of this 1983 Yale graduate course was to make some recent results in modular representation theory accessible to an audience ranging from second-year graduate students to established mathematicians.After a short review of background material, three closely connected topics in modular representation theory of finite groups are treated: representations rings, almost split sequences and the Auslander-Reiten quiver, complexity and cohomology varieties. The last of these has become a major theme in representation theory into the 21st century.Some of this material was incorporated into the author's 1991 two-volume Representations and Cohomology, but nevertheless Modular Representation Theory remains a useful introduction.