A self-contained discussion of quasilinear hyperbolic PDEs and systems, this book includes carefully chosen physical examples in gas dynamics and shallow water theory. It introduces the necessary mathematical concepts in the first three chapters, which cover wave propagation problems and the issues to be developed in the remainder of the text. The book describes the applications of the characteristic approach, singular surface theory, asymptotic methods, self-similarity and group theoretic methods, and the theory of generalized functions to several concrete physical examples from radiation gas dynamics, magneto gas dynamics, and nonequilibrium flows.