Nobel Laureate Steven Weinberg continues his masterly exposition of quantum field theory. This third volume of The Quantum Theory of Fields presents a self-contained, up-to-date and comprehensive introduction to supersymmetry, a highly active area of theoretical physics that is likely to be at the center of future progress in the physics of elementary particles and gravitation. The text introduces and explains a broad range of topics, including supersymmetric algebras, supersymmetric field theories, extended supersymmetry, supergraphs, nonperturbative results, theories of supersymmetry in higher dimensions, and supergravity.