Nonlinear wave equations belong to a typical category of nonlinear evolutionary equations that is of great theoretical significance and practical value.

The whole book has got fifteen chapters in all. The first seven serve as a prelude for later discussions, but still have their own meanings and values. Among the later eight chapters, five discuss the global existence and the lower bound estimates of life-span for classical solutions in all possible situations by adopting the global iteration method, including the proof of global existence of classical solutions under the hypothesis of the null condition; two focus on demonstrating the sharpness of the obtained lower bound estimates of life-span; and the last chapter entails relevant applications and extensions.