THE incorporation of nitrogen in oxide glasses can lead to improved physical properties such as hardness and refractive index(1-4); one might accordingly expect to see a further improvement in glasses containing nitrogen as the only anion. But while there are now many examples of non-oxide glasses in the halide and chalcogenide families(5-8), the formation of pure nitride glasses has not hitherto been demonstrated. Here we report the formation of glasses in the system Li3N-Ca3N2-P3N5, by the rapid quenching of fused mixtures of the nitrides at high pressures. The use of high-pressure conditions prevents thermal decomposition of the nitride mixtures to gaseous nitrogen. The new nitride glasses are stable in air, have remarkably high refractive indices (1.97-2.0), hardness exceeding that of silica glass, and high glass transition temperatures (T-g > 700 degrees C).