Hans-Werner Henn, 
Cohomology of Groups and Unstable Modules over the Steenrod Algebra. 

Abstract : The presence of Steenrod operations in the mod - $p$ cohomology 
ring $H^*(BG;\FF_p)$ of the classifying space $BG$ of a group $G$ allows to
understand qualitative features of this ring, at least for a large class of 
groups including all compact Lie groups but also for many discrete groups like 
arithmetic groups, mapping class groups and automorphism groups of free groups.
We explain the relevant theory of unstable modules over the Steenrod algebra 
and indicate how this general theory can be used in the qualitative and 
quantitative study of group cohomology.