Space Shuttle astronauts are exposed to both the “trapped” radiation and the galactic cosmic radiation environments. In addition, the sun periodically emits high-energy particles which could pose a serious threat to flight crews. NASA adheres to federal regulations and recommended exposure limits for radiation protection and has established a radiological health and risk assessment program. Using models of the space radiation environment, a Shuttle shielding model, and an anatomical human model, crew exposure estimates are made for each Shuttle flight. The various models are reviewed. Dosimeters are worn by each astronaut and are flown at several fixed locations to obtain in-flight measurements. The dosimetry complement is discussed in detail. A comparison between the premission calculations and measurements is presented. Extrapolation of Shuttle experience to long-duration exposure us explored.