The basics of aerothermodynamics are treated in this book with special regard to the fact that outer surfaces of hypersonic vehicles primarily are radiation cooled. The implications of this fact are different for different vehicle classes. In any case the properties of both attached viscous and separated flows are of importance in this regard. After a discussion of flight environment and transport phenomena in general, the most important aerothermodynamic phenomena are treated. Thermal surface effects are particularly considered, taking into account both radiation cooling and/or active cooling, for example of inner surfaces. Finally the simulation means of aerothermodynamics are discussed. Computational methods and their modelling problems as well as the problems of ground facility and flight simulation, including the hot experimental technique, are treated.