Satellite altimetry continues to have an extraordinary impact on the Earth sciences. It is sure to be considered the most important new observing tool for marine geophysics and geology to emerge in recent times. Spacecraft that have used and are currently using radar altimeters to map sea‐surface topography, and thereby marine gravity, include Geos‐3, Seasat, Geosat, ERS‐1, and Topex/Poseidon. To date, however, only Geosat altimeter data have possessed both the accuracy and density of coverage necessary to clearly resolve tectonic details in the marine gravity field on a global basis.