This book presents the current state of the theory of nonlinear oscillations and waves. From a single point of view, oscillatory and wave processes, both periodic and chaotic, are considered in systems of a wide variety of physical nature. It has been shown that such popular and rapidly developing sciences in recent years as nonlinear dynamics, soliton theory and synergetics, which are often studied independently of each other, are actually components of the theory of oscillations and waves.