  Numerous topics in three and four dimensional supersymmetric gauge theories
are covered. The organizing principle in this presentation is scaling
(Wilsonian renormalization group flow.) A brief introduction to scaling and to
supersymmetric field theory, with examples, is followed by discussions of
nonrenormalization theorems and beta functions. Abelian gauge theories are
discussed in some detail, with special focus on three-dimensional versions of
supersymmetric QED, which exhibit solitons, dimensional antitransmutation,
duality, and other interesting phenomena. Many of the same features are seen in
four-dimensional non-abelian gauge theories, which are discussed in the final
sections. These notes are based on lectures given at TASI 2001.
