Many important geophysical processes inaccessible to our direct observation have been studied by measuring subtle deformations of the Earth's surface. Orbital satellites can now provide precise measurements of surface changes for studying these processes worldwide. One major contribution in this area has been the development of interferometric synthetic aperture radar (InSAR), which can provide more spatially dense and accurate deformation measurements than have been possible previously with radar systems. The most important advances demonstrated to date have been related to tectonic (seismic and volcanic) processes, and to glacier and ice sheet motions mapped in the environmentally sensitive and diagnostic polar regions. Many other ground subsidence phenomena are under investigation, and promise continued significant results.