This text presents a series of thematic chapters together with chapters on representative groundwater systems in Europe which illustrate the main processes and evolution of water quality. It brings together the research of a consortium of leading European scientists who have conducted detailed studies of water quality in Europe. It includes a synthesis of findings, highlighting the thematic and regional results, with recommendations regarding aquifer evaluation, indicators, monitoring, and drinking water standards. It creates a key reference work on natural water quality of aquifers, at a time when the Groundwater Directive (GD) will shortly be brought in to supplement The European Water Framework Directive (WFD) to ensure good status of groundwater.