Urbanization modifies underlying groundwater systems. This often leads to adverse hydrological, water quality, geotechnical, and socio-economic effects which jeopardize sustainability. Indeed, for many urban aquifers world-wide, we do not know whether there even exist socially-acceptable sustainable hydrological systems. Given that around 50% of the world population live in cities, and that urban populations are expanding rapidly, the issues are important and becoming increasingly urgent. To reduce the effects of such impacts, management is required irrespective of whether the groundwater is to be used or not. This management must be based on a sound technical understanding of the interacting processes involved. The forty papers in the present volume explore the state of this understanding in the context of a wide range of countries (and therefore cultures), climates, and geologies. They are divided into topic areas covering flow, chemical water quality, biological water quality, remediation, engineering, and socio-economics. An initial section sets the scene with a range of integrated regional-scale studies. The volume will be of interest to practicing groundwater specialists in industry and research. We hope that it will also provide an insight into groundwater issues for other urban specialists, including planners: without communication between the disciplines involved, progress towards acceptable urban sustainability will be slow.