The U.S. Navy satellite Geosat has provided the first altimeter data set that is both long term and global in coverage. This special issue of JGR-Oceans demonstrates the high level of interest in this unprecedented data stream. Geosat data contain information on sea surface topography, sea state, and wind speed. Also present in the sea level data are systematic errors arising from propagation effects and uncertainty in the satellite ephemeris. A major effort of the community that uses altimeter data is to understand the limitations of Geosat data arising from these errors and devise means to overcome them. Thus many papers in this special issue deal with algorithms and verification in an effort to establish the scale of the problems to which Geosat data can be applied both now and with future improvements. The scientific results presented here amply illustrate the value of the data already released. Another facet of Geosat not reported in any paper has been the unselfish cooperation of the satellite geodesy-altimetry community. Investigators in the United States and aboard are freely sharing their results, ideas, and computer programs on an open basis, making participation in the Geosat effort a great pleasure as well as professionally rewarding.