TOPEX/POSEIDON is a satellite mission that will use a radar altimeter system to measure sea level, which will reveal ocean topography and enable study of the circulation of the world's oceans. The measurement will also be useful for the study of ocean tides and marine geodesy and geophysics. Figure 1 is an artist's rendition of the TOPEX/POSEIDON satellite flying above the Earth. The mission is jointly conducted by the National Aeronautics and Space Administration (NASA) and the French space agency, Centre National d'Etudes Spatiales (CNES). Current plans call for launch of the satellite by an Ariane launch vehicle in the summer of 1992. The primary mission will last for 3 years, with the possibility of extending the mission 2 more years. The mission has been coordinated with a number of international oceanographic and meteorological programs, including the World Ocean Circulation Experiment (WOCE) and the Tropical Ocean and Global Atmosphere Programme (TOGA), both of which are sponsored by the World Climate Research Programme (WCRP). The observations of TOPEX/POSEIDON are timed to provide a global perspective for interpreting the in situ measurements collected by these programs, which will in turn be combined with satellite observations to achieve a global, four-dimensional description of the circulation of the world's oceans. Born et al.  gives the background for the early phase of the mission's development. This article gives an updated overview of the mission as it is currently configured for launch in the next year.