The papers in this volume represent most of the contributions to the Symposium on the Physics of Opto-Electronic Materials held at the General Motors Research Lab oratories in Warren, Michigan, on October 4, 5 and 6, 1970. The purpose of this Symposium was to examine the current status of knowledge related to the controlled alteration of the optical properties of solids through exter nally-applied agencies, with the aim of assessing possible future directions of scientific effort to achieve efficient, practical control of light. Since the advent of the laser, the scientific community has been motivated to explore, with a renewed vigor, methods of modulating light, and in the last decade several applications of the electrooptic effect in single crystal solids have been real ized. During this same period of time the list of recognized optical modulation ef fects in solids (exclusive of the ordinary electrooptic effects) has grown rapidly, and recently dramatic demonstrations of light modulation by liquid crystal and ferro electric ceramic materials have captured the attention of the scientific community. Unlike the single-crystal electrooptic effects which are quite suitable for modulation of coherent laser light, these latter materials promise relatively inexpensive approaches to the modulation of light from ordinary incoherent light sources. It was these new vistas of light modulation - and how they fit into our current understanding of the optical properties of solids - that the symposium addressed.