Silicon nitride ceramics are finding increased usage as wear-resistant components in machines. As such, these ceramic surfaces encounter a variety of counterface materials and operating environments. The purpose of this study was to examine the tribological properties of silicon nitride in sliding contact with itself, nodular cast iron, 316 stainless steel, and Inconel 718 in air and vacuum. The laboratory tests have shown that the kinetic friction coefficients were higher in vacuum than in air. Higher friction did not lead to higher wear in all cases. These results are discussed in terms of the mechanical and chemical properties of the materials, the operative wear mechanisms, and the implications of their compatibility in engineering applications.