The development of the shock tunnel is reviewed, its present capabilities are discussed, and future prospects are outlined. The ability of the shock tunnel to produce air flows at stagnation temperatures and pressures associated with hypersonic flight has been well established. The chief difficulty has been the short millisecond testing time. The tailored-interface technique has increased the available testing time. This extension, plus the development of rapid-response instrumentation, now permits the accurate measurement of pressures, forces, and heat transfer rates. The hypersonic shock tunnel in its present form duplicates re-entry flight conditions for hypersonic vehicles over an important area of the re-entry flight. For some regions partial simulation must be resorted to. However, the flexibility of the shock tunnel operations permits a wide range of simulation conditions to be studied. The shock tunnel has exceeded expectations both as to its range of performance and scope of testing. Exploratory experiments have demonstrated the usefulness of the shock tunnel for the investigation of hypervelocity rarefied-gas flows associated with the re-entry of manned vehicles.