From the San Francisco Bay Delta to the Florida Everglades and from upstate New York to Houston, illustrative case studies describe three basic mechanisms by which human manipulation of groundwater causes land subsidence: groundwater withdrawal, dewatering and oxidation of organic soils, and dissolution collapse of susceptible materials. In the United States, subsidence due to these mechanisms affects more than 40,000 square kilometers in 45 states and causes at least $125 million in annual damage. Interferometric Synthetic Aperture Radar (InSAR) is a powerful new tool for assessing and mitigating subsidence.