Hypersonic flight (typically over five times the speed of sound) has the potential of changing several aspects of transport and weapon use. Hypersonic flight also poses new questions in design of vehicles. Perhaps most so in relation to the propulsive system if the vehicle is to manage sustained cruise. Here we present an overview of airbreathing engines for several ranges of speed. The general requirements for a hypersonic jet engine is presented as well as those for a testing facility apt for hypersonic propulsion research. Three different methods for simulating one type of hypersonic engine, known as the supersonic ramjet - scramjet, are presented. The methods range from detailed high-resolution fluid dynamic models to a zerodimensional model for performance estimates. Finally, possibilities, difficulties and future needs within the area of hypersonic jet propulsion are discussed.