The Geometry of Supersymmetric Gauge Theories in Four Dimensions

We review the relations between (twisted) supersymmetric gauge theories in four dimensions and moduli problems in four-dimensional topology, and we study in detail the non-abelian monopole equations from this point of view. The relevance of exact results in N=1 and N=2 supersymmetric gauge theories to the computation of topological invariants is emphasized. Some background material is provided, including an introduction to Donaldson theory, the twisting procedure and the Mathai-Quillen formalism.