  These are lecture notes from the IMPANGA 2010 Summer School. The lectures
survey some of the main features of equivariant cohomology at an introductory
level. The first part is an overview, including basic definitions and examples.
In the second lecture, I discuss one of the most useful aspects of the theory:
the possibility of localizing at fixed points without losing information. The
third lecture focuses on Grassmannians, and describes some recent positivity
results about their equivariant cohomology rings.
