Nonlinearities and optics, optoelectronics and fiber communications are discussed systematically in this book. In a unified theoretical treatment, the book addresses the three categories of materials: fibers, semiconductors, and nonlinear crystals. In each case emphasis is placed on the nonlinear character of their refractive indices and optical absorption. The text also gives an in-depth analysis of the uses and limitations of phontonic nonlinearities with regard to wavelength division multiplexing and high-speed fiber communications. It will be of interest to graduate students as well as researchers and engineers in the fields of nonlinear optics and optical communications.