Reduction in the volume of groundwater in storage in the subsurface is a natural outcome of development and withdrawal through wells of large quantities of groundwater. In some cases, the depletion is so large as to cause reduced well yields, deterioration of water quality, reduced reserves, unsustainability of pumpage, and environmental damage (through subsidence and reduced discharge of freshwater to springs, lakes, streams, wetlands, and/or estuaries). But the magnitude of volume of depletion is rarely assessed. In this session, we present papers that • Quantify the magnitude of depletion in developed aquifer systems • Offer new methods to estimate depletion • Describe effects of depletion • describe management approaches to deal with or offset depletion • Illustrative case histories from around the world.