Volcano geodesy is the branch of geodetic science that deals with the changing shapes of volcanoes, whether large or small, deep-seated or surficial. Together with seismicity and volcanic gas flux, deformation of the ground surface can be a key indicator of subsurface conditions and processes at volcanoes—information that not only improves scientific understanding of magmatic systems but also is useful for assessing volcano hazards and mitigating their potential consequences. To take full advantage of such information requires detailed characterization of the deformation field in space and time. Currently, no single geodetic technique is capable of providing both the high spatial and temporal resolution required. However, important advances have been made recently by combining information from real-time in situ sensors such as continuous GPS, strainmeters, and tiltmeters with repeated campaign-style GPS, microgravity, interferometric synthetic aperture radar (InSAR), lidar, and photogrammetric observations. Continuous real-time data constrain the timing but not necessarily the spatial extent and pattern of deformation, whereas InSAR provides detailed spatial information but only at intervals of several days to weeks. Repeated microgravity surveys, when combined with independent measurements of surface height, are uniquely sensitive to changes in subsurface mass distribution and therefore can be used to distinguish among processes driven by magma, hydrous fluids, or gas. Simultaneous analysis of multiple geodetic datasets, especially when guided by information from global volcano databases and numerical simulations of volcanic processes and products, can provide a statistical basis for outcome prediction and serve as a guide for additional observations. In the foreseeable future, interactions among magmatic, tectonic, and hydrothermal systems will be monitored and modeled at regional scale in real time, enabling new insights into Earth’s subsurface environment.