Abstract: Precise measurements of ground deformation have become increasingly common as large networks of GPS receivers and borehole strainmeters have been established over the last decade. Complementing this continuous record are comparatively infrequent but spatially dense images of ground deformation from radar satellites, and a long historical record of leveling, Electronic Distance Meter, triangulation, and tilt data. Deformation can arise from tectonic and volcanic forces and from human activities such as aquifer withdrawal or geothermal exploitation. Mathematical models of how the crust deforms in response to different physical processes are required to characterize driving processes and constrain source location, size, orientation, and strength. This information is valuable for hazards forecasting and mitigation.