Hydrogeology of Crystalline Rocks deals with deep groundwater in the granite and gneiss basement of the continents. It has become evident during the past years that highly mineralized water is present in an interconnected fracture network of the basement. Thus, the upper part of the crust of the continents can be viewed as an aquifer and investigated with tools common in hydrogeology. This book presents accounts on water-conducting features of crystalline rocks and summarizes the hydraulic properties of the basement. The volume includes reviews, new data and research on the often remarkable chemical composition of deep groundwater. Microbial processes in the deep basement aquifer are probably more important than previously thought. Two contributions focus on this recent extension of research of the biosphere to greater depth in the Earth. This book represents the first multidisciplinary and integrated account of deep groundwater hydrology in crystalline basement. It is of interest to hydrologists and hydrogeologists working with water in crystalline rocks, but also to solid earth geophysicists, geochemists and petrologists with an interest in fluids in the crust. Scientists involved in nuclear waste disposal programs and geothermal energy development will find a wealth of stimulating ideas in this volume.