This volume is based on lectures and contributed papers presented at the Eleventh Course of the International School of Materials Science and Tech­ nology that was held in Erice, Sicily, Italy at the Ettore Majorana Center for Scientific Culture during the period 6-17 July 1986. The subject of the course was "Electro-optic and Photorefractive Materials: Applications in Sig­ nal Processing and Phase Conjugation" . The fields of electro-optics and photorefraction have developed rapidly since the invention of lasers just over twenty-five years ago. The possibil­ of altering the optical properties of a material by electric fields or by ity optical waves is of great importance for both pure science and for practical applications such as optical signal processing, telecommunications and opti­ cal display devices. These effects allow us to manipulate (modulate, deflect) and process a given light wave. Modulation, deflection and processing of light waves by means of the electro-optic effect is of fundamental importance in fiber optic telecommuniC1. tions and sensor systems w here the light signals can be processed prior or subsequent to transmission through the fibers. Thin film electro-optic materials with suitable electrode arrays on· the surface of the wave-guiding structures result in a technology often referred to as inte­ grated optics. In principle, integrated optics devices allow miniaturization and integration of many operations onto a single chip. The photorefractive effect, defined as a photo-induced change of the in­ dices of refraction, was the other topic treated in this course.