Nonlinear optics is the study of the interaction of intense laser light with matter. This Third Edition has been rewritten to conform to the standard SI system of units and includes comprehensively updated material on the latest developments in the field. The book introduces the entire field of optical physics and specifically the area of nonlinear optics. It focuses on the fundamental issues including the electromagnetic origin of optical phenomena, the quantum mechanical description of the optical properties of matter, the role of spatial symmetries in determining the optical response, causality and Kramers Kronig relations, and ultrafast and high intensity optical effects.