Ceramics have been an important class of materials because of their inertness and heat-resistant properties. Applications based on unique properties of ceramic materials range from refractory bricks and crucibles for molten metals to miniature electronic devices; from nuclear fuels and control elements to magnetic memory units. This chapter describes the ceramic materials such as alumina, beryllia, zirconia, mullite, cordierite, silicon carbide, and silicon nitride. It tabulates crystal chemical, thermodynamic, physical, mechanical, thermal, and electrical properties of the ceramic materials. The crystal chemical and thermodynamic properties are independent of processing conditions and are listed separately from the other properties. The physical, mechanical, thermal, and electrical properties are a function of the processing conditions. These properties can be modified through process changes to meet specifications for different applications. To show these effects, data on the physical, mechanical, thermal, and electrical properties for some of the materials are given for different levels of density and purity.