Beginnings of group cohomology

Cohomology theory is a powerful mathematical tool. This theory applied to topology is a part of algebraic topology, which associates algebraic invariants to topological spaces. In this article, we give a brief outline of group cohomology. R Sridharan has been an Adjunct Professor at the CMI, Chennai since retiring from TIFR, Bombay in 2000 where he was a senior professor. He is also an INSA senior scientist now. His scholarship permeates to literature (English and Sanskrit) and philosophy as well. Many of the algebraists in the country were his students. Dedicated to my teacher S Eilenberg