In Part A of this chapter we consider one-dimensional models both simple and complex. In Part B we go to the classical theory for isotropic, multidimensional behavior. Here, we extrapolate from the one-dimensional case to the multidimensional case in a manner that parallels what we did in Chapter 5 for linear elastic behavior. In the development we utilize the discontinuity functions (i.e., the step, delta, and doublet functions) as well as the Laplace transformation. These topics are reviewed in Appendices II and III, respectively.