This booklet presents a study of one-dimensional waves in solids which can be modelled by nonlinear wave equations of different types. The factorization method is the main tool in this analysis. It allows for an exact or at least asymp­ totic decomposition of the wave(s) under consideration in terms of first order multipliers. Chapter 1 provides a general introduction. It presents some well-known results on characteristics, Riemann invariants, simple waves, etc. The main result of Chap. 1 is Theorem 1.3.2. (Sect. 1.3.2) which establishes the possibility of exact factorization of the nonlinear wave equation EPa(a) 1 EPa _ 0 Ij(l-u- x2 with constant coefficients. This theorem permits one to construct further factor­ izations of more complicated wave equations which the reader will meet in the following chapters. Chapter 2 is devoted to short wave processes in inhomogeneous media, the main result being the uniform asymptotic factorization of nonlinear wave equa­ tions with variable coefficients and the description of corresponding single-wave processes without the usual assumption of a small wave amplitude.