This is a self-contained introduction to a new field of applied physics on the frontier between integrated optics and non-linear wave dynamics. It is intended to help make use of the novel phenomena of non-linear optics in the design of new all-optial circuits. The book mainly deals with third-order non-linear optical phenomena in layered structures, guiding interfaces, and channel waveguides. In particular attention is drawn to the concepts of energy dependent periodicity, gyrotropy, reflection, mode conversion, and non-reciprocity. An indespensable text for those requiring a structured explanation of the phenomena as well as information about the latest advances in a new generation of devices.