Nonlinear Optical Parametric Processes in Liquids and Gases focuses on the parametric processes that occur in liquids and gases. This book examines the mathematical results that are intended mainly for their usefulness in quantifying the physical interpretations of the various concepts to actual systems. Comprised of six chapters, this text starts with a discussion on the nonlinear optical processes, and then explores the basis for nonlinear optical interactions. This book describes the various third-order frequency mixing processes and the basic properties of nonlinear interactions, including phase matching and resonant enhancement. Other chapters consider the processes of frequency mixing and harmonic generation that are used as illustrations of the basic principles. The final chapter explores the applications of several nonlinear optical interactions, with a focus on the use of nonlinear optical processes to control the propagation of optical waves or to obtain information about a material system. This book is intended for researchers and readers engaged in the study of university-level mathematics, electromagnetic theory, and atomic physics.