A review is presented of experimental studies and numerical calculations conducted to examine the separate and combined effects of viscous inviscid interaction and nonequilibrium air chemistry on the aerothermal characteristics of complex flowfields over simple model configurations and on hypersonic vehicles operating in the low density, laminar and turbulent flow regimes. The experimental studies were conducted in the LENS I and II Shock Tunnels and the newly constructed LENS X Expansion Tunnel. Measurements made in these tunnels are compared with predictions from Navier-Stokes calculations as well as solutions based on the method of characteristics. The studies in low density flows conducted in the LENS I facility and their comparison with recent DSMC and Navier-Stokes predictions are summarized. We then review recent experimental and numerical studies to evaluate vibrational nonequilibrium and real gas effects on a double cone configuration. Surface and flowfield measurements are presented to demonstrate important characteristics of tripped hypersonic flows generated to create turbulent boundary layer flows for the purpose of simulation, and to create the desired turbulent boundary layer flow into scramjet engine inlets. These studies demonstrated the importance of correctly selecting the size and geometry of the trips. Preparations are being made for studies of flow vitiation and real gas effects in ground tests of scramjet engines.