Waves occur naturally in a vast number of scientific or engineering situations. Ripples on a pond, the light we see and the oscillations of bridges and buildings can often be described as solitary or interacting waves. Wave theory is therefore one of the most important branches of pure and applied science. In this book, Lev Ostrovsky and Alexander Potapov consider linear and nonlinear waves such as solitons, waves in inhomogeneous media and many others. They discuss modulated waves - those characterized by a slow variation of the macroscopic parameters of amplitude, frequency, and profile. Most of the fundamentals of wave theory may be understood by considering this class of waves. Theoretical analysis is supported by examples from different branches of physics: electrodynamics, fluid mechanics, acoustics, optics and the mechanics of solids.