ABSTRACT The Edwards Aquifer along the Balcones fault zone is in a rapidly growing, urbanizing area. Urbanization creates major hydrogeological impacts, generally increasing impervious cover and flooding intensity, water demands, groundwater recharge, and temperatures both above and below the land surface; covering springs and small streams; altering the porosity and permeability fields; and contaminating groundwater, surface water, and soils. Urbanization also alters topography, natural flora, and the local climate. Several of these effects have either been documented or predicted for the Edwards Aquifer. Groundwater recharge from leaky utility systems and irrigation return flow is significant, particularly during times of low rainfall. The hydraulic properties of the epikarst, particularly the permeability field, can be highly modified. Aquifer water quality remains excellent, but increased anthropogenic chemical nitrate and chloride concentrations, and occasional bacteriological contamination have been observed. The eventual effects of these changes on the aquifers’ unique ecosystems is not known. Urbanization and urban sprawl are projected to increase, which will continue to alter the Edwards Aquifer system physically, chemically, and biologically. Understanding of these changes, their causes, and their effects is necessary to addressing the critical and growing environmental and water-resources issues of urban areas in the coming century.