Satellite altimetry is valuable for measuring sea surface topography and global ocean circulation, but only if the satellite's orbit can be computed within a few centimeters. A tracking system called DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) was developed in the early 1990s for this purpose. It provides precise orbit determination and site positioning and overcomes the limitations of previous tracking systems: insufficient measurement precision and incomplete orbit coverage. DORIS' capabilities are not limited to precise orbit determination, however. It can also be used for other geodetic applications, including the measurement of large-scale tectonic motions.