Nonlinear Optics (NLO) deals with the interactions of applied electromagnetic fields in various materials to generate new electromagnetic field altered in phase, frequency, amplitude or other physical properties. The nonlinear optical properties of materials play a role in many applications. The second order nonlinear response has a wide range of applications in the field of telecommunications; optical computing, storage and information processing etc. The third-order nonlinear optical response is important in all-optical switching, signal processing, and ultrafast optical communications. The objectives of the book covers synthesis and growth of bulk single crystals of organic nonlinear optical materials; Characterization of grown crystals by X-ray, thermal, mechanical and spectral techniques; Investigating the linear and nonlinear optical properties of the materials; provides a firm relationship between nonlinear optical property and molecular structure of the materials. The book consists of eight chapters. The extensive studies of the above objectives are presented in these chapters.