Topological Aspects of Four-Manifolds -- The Theory of Donaldson Invariants -- The Theory of Seiberg-Witten Invariants -- Supersymmetry in Four Dimensions -- Topological Quantum Field Theories in Four Dimensions -- The Mathai-Quillen Formalism -- The Seiberg-Witten Solution of N = 2 SUSY Yang-Mills Theory -- The u-plane Integral -- Some Applications of the u-plane Integral -- Further Developmenā¦