The results of an experimental study of the Mach reflection of shock waves in argon, nitrogen, air, and carbon dioxide are presented. Various forms of Mach reflection are considered, taking into account the occurrence of simple and double Mach reflections and phenomena related to the transition between them. The experimental data are compared with the results of a theoretical analysis. Questions related to the transition between Mach and regular reflection are also investigated. Schlieren photographs of Mach reflection are presented, and pressure measurements conducted with the aid of piezoelectric gauges are reported.