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.