TOPEX/POSEIDON is a satellite mission that will use the technique of radar altimetry to make precise measurement of sea level with a primary goal of studying the global ocean circulation . The mission represents the culmination of the development of satellite altimetry over the past two decades. The major thrust of the mission is a commitment to measuring seal level with an unprecedented accuracy such that the small-amplitude, basinwide sea level changes that bear significant effects on global change can be detected. The mission will be conducted jointly by the United States National Aeronautics and the Space Administration and the french space agency, Centre National d'Etudes Spatiales. The 3- to 5-year mission will study the long-term mean and variability of ocean circulation. This document provides brief descriptions of the planned investigation s as well as a summary of the major elements of the mission.