This graduate-level textbook gives an introductory overview of the fundamentals of quantum nonlinear optics. It deals with the organization of radiation field, interaction between electronic system and radiation field, statistics of light, mutual manipulation of light and matter, laser oscillation, dynamics of light, nonlinear optical response, and nonlinear spectroscopy, as well as ultrashort and ultrastrong laser pulse. In addition, latest results of the frontier of this science are presented. Problems and solutions help the reader to master and review the material.