The projects treated at the 1991 ICASE Summer Workshop on Instability, Transition and Turbulence at the NASA Langley Research Center focused on nonlinear aspects of the boundary-layer transition and on theory and modeling of turbulence, with emphasis on high-speed flows. Groups of workshop participants dealt with such topics as experimental methods, asymptotics, advanced stability, simulation, receptivity, and turbulence theory and modeling. This volume presents a summary of their results.