After some decades of comparative neglect, changes in mean sea level relative to land (RSL) are now appreciated by oceanographers and geophysicists as an important integral parameter of ocean climate and vertical land movement that is fairly easy to measure for long periods. Interest has been raised by the relevance of RSL to “El Niño” events, as shown by the new Pacific island network operated by the University of Hawaii, and by several studies of recent secular rise in global RSL in relation to changes in temperature and glaciation. Monthly RSL maps for the entire tropical Pacific are currently issued in near real time by the Integrated Global Ocean Station System Sea Level Pilot Project. A global network of tide gage stations has recently been proposed by the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization in support of the Tropical Ocean Global Atmosphere (TOGA) and World Ocean Circulation Experiment (WOCE) campaigns.