  These are expository lectures reviewing
  (1) recent developments in two-dimensional Yang-Mills theory, and
  (2) the construction of topological field theory Lagrangians. Topological
field theory is discussed from the point of view of infinite-dimensional
differential geometry. We emphasize the unifying role of equivariant cohomology
both as the underlying principle in the formulation of BRST transformation laws
and as a central concept in the geometrical interpretation of topological field
theory path integrals.
