The paper presents the results of a characterization study of selected materials for possible use as laser windows. The preliminary materials selection was based on known or calculated optical properties at the wavelengths of interest and the availability of the materials in sufficient quantity and size. The characterization includes optical, mechanical, and thermal property determinations necessary for the systems designer to make proper selection of a window material based on system requirements. The materials presently under consideration include A1203 (sapphire), Si02 (fused silica), Y3A15012 (YAG), MgO, ZnS, ZnSe, CaF2, BaF2, SrF2, LiYF4 (YLF) and various fluoride glass compositions. The optical properties for the wavelengths of interest will be presented and the problems encountered when designing with brittle materials will be discussed.