ABSTRACTDielectric insulator materials have played a critical role in the development of high peak power solid state lasers for use in inertial confinement fusion research: as laser gain media; as transparent substrates for lenses, mirrors, and polarizers; and as active optical materials in nonlinear harmonic generators and electro-optical devices. Materials have been developed which have exceptionally high resistance to damage in the presence of intense optical beams (> GW/cm2) and which possess other properties which optimize their functions in the laser systems. Fusion lasers built to date have been designed for “single shot” operation, and the dielectric insulator materials developed for use in them have had to function under only extremely low average power loading. As we look to the future, fusion laser systems will be required to operate repetitively (few Hz) and deliver high average power output (> MW) at an efficiency greater than 10 percent. Insulator materials for use in these systems must be selected and developed on the basis of their combined mechanical, thermal, and optical properties. In this presentation, I will summarize the important characteristics of currently used insulator materials, identify figures of merit for materials needed in future systems, and outline a methodology for identifying and evaluating new materials meeting the stringent performance requirements of future fusion laser systems.