The glancing interaction between an oblique shock wave and a turbulent boundary layer has been studied experimentally using a variable-incidence wedge mounted from the side wall of a supersonic wind tunnel. The Mach number was 2·3 and the Reynolds number 5 × 104, based on the 99·5 % thickness of the boundary layer just upstream of the interaction region. The study includes oil flow pictures, vapour and smoke-screen photographs, wall-pressure distributions and local heat-transfer measurements. The results suggest that the complicated interaction region involves two viscous layers: an induced layer formed from fluid initially in the boundary layer growing along the wedge surface near the root, and the thick turbulent layer on the tunnel side wall. The mutual interference between these layers is described, separation is defined and a discussion of incipient separation is included.