Waves are ubiquitous in nature. We are all familiar with water waves, sound waves, electromagnetic and seismic waves. It is fair to say that every area of science and technology has sources of problems involving some type of wave motion. As a result, a large arsenal of analytical techniques has been developed to describe and analyze linear and nonlinear wave phenomena. And, of course, the numerical simulation of wave motion, mainly the numerical solution of the partial differential equations of wave theory, has been at the center of attention of computational scientists since the advent of the modern computer era.