This volume contains four comprehensive articles. Milton Van Dyke's article, "Slow Variations in Continuum Mechanics," is a systematic approach to a wide range of flow problems where the motion is predominantly one-dimensional. The simplest one-dimensional approximation to each such problem is derived as the lowest order contribution in an appropriate perturbation expansion. Julius Miklowitz has prepared a detailed survey of three areas of wave mechanics: (1) elastic waveguides, (2) elastic pulse scattering by cylindrical and spherical obstacles, and (3) the two-dimensional wedge and quarter plane. His article is entitled "Modern Corner, Edge, and Crack Problems in Linear Elastodynamics Involving Transient Waves." Hans Ziegler and Christoph Wehrli have made an ambitious attempt to unify a wide class of constitutive laws for elastic-plastic solids within the framework of thermodynamics in their article, "The Derivation of Constitutive Relations from the Free Energy and the Dissipation Function." (...)