This book is an expanded version of the Hermann Weyl Lectures given at
the Institute for Advanced Study in January 1986. It outlines some of
what is now known about irreducible unitary representations of real
reductive groups, providing fairly complete definitions and references,
and sketches (at least) of most proofs.
The first half of the book is devoted to the three more or less
understood constructions of such representations: parabolic induction,
complementary series, and cohomological parabolic induction. This
culminates in the description of all irreducible unitary representation
of the general linear groups. For other groups, one expects to need a
new construction, giving "unipotent representations." The latter half of
the book explains the evidence for that expectation and suggests a
partial definition of unipotent representations.