A theoretical study of the effects of the wall boundary layer on the supersonic flow around a sharp convex corner is presented. Fundamentally different methods of analysis are adopted for laminar and for turbulent boundary layers. In the case of interactions involving laminar boundary layers, an analysis based on the use of classical boundary layer theory is used. Results of numerical calculations carried out using this analysis to predict the effects of the major governing parameters are presented. In all cases, a considerable upstream and downstream influence is predicted. A simplified form of this analysis, closely related to that of Curle, is also presented, this analysis leading to a simple set of explicit equations describing the flow quantities in the interaction region. Comparison of the simplified analysis with results obtained from the full analysis indicated, as is to be expected, that the simplified analysis will only give acceptable results for small expansion angles and moderate Mach numbers. In the case of turbulent boundary layer interactions, an analysis based on the assumption that there is no upstream influence and that the major portion of the expansion occurs in an effectively inviscid manner is adopted, the flow properties being calculated by the method of rotational characteristics. (Author).