"Theory of Diffraction: Heuristic Approaches" outlines the asymptotic methods in the theory of diffraction, which manifest their strong heuristic nature, including the geometrical theory of diffraction by J.B. Keller, the physical theory of diffraction by P.Ya. Ufimtsev, the parabolic wave-equation method by Leontovich and Fock, which forms the basis for quasi-optics, the complex geometrical optics as well as the Maslov's, Kravtsov-Ludwig's and Orlov's asymptotic methods for a caustic-wave-fields description. The book is addressed to engineers, applied physicists and students, who need a compact, without complicated mathematics, comprehensive outline of the most effective methods of diffraction theory, capable of describing the lion's share of applied problems.