The Upper Atmosphere Research Satellite (UARS) is a NASA program aimed at improving our knowledge of the physical and chemical processes controlling the stratosphere, mesosphere, and lower thermosphere, emphasizing those levels that are known to be particularly susceptible to change by human activities. The spacecraft was launched by the Space Shuttle Discovery on September 12, 1991, into a near-circular orbit at 585 km altitude and 57¿ inclination. Measurements include vertical profiles of temperature, many trace gases, and horizontal wind velocities, as well as solar energy inputs. Many of the limb-scanning instruments can measure to as high as 80¿ latitude, providing near-global coverage. The mission is supported by a large international correlative measurement program, yielding data both for validation of the UARS measurements and for complementary scientific studies. A dedicated data system provides rapid processing to geophysical quantities and makes these data available to UARS scientists.