Groundwater resources are facing increasing pressure from consuming and contaminating activities. There is a growing awareness that the quantitative and qualitative preservation of groundwater resources is a global need, not only to safeguard their future use for public supply and irrigation, but also to protect those ecosystems that depend partially or entirely on groundwater to maintain their species composition and natural ecological processes. Known as groundwater dependent ecosystems (GDEs), they have been a fast-growing field of research during the last two decades. This book is intended to provide a diverse overview of important studies on groundwater and ecosystems, including a toolbox for assessing the ecological water requirements for GDEs, and relevant case studies on groundwater/surface-water interactions, as well as the role of nutrients in groundwater for GDEs and ecosystem dependence (vegetation and cave fauna) on groundwater. Case studies are from Australia (nine studies) and Europe (12 studies from nine countries) as well as Argentina, Canada and South Africa. This book is of interest to everybody dealing with groundwater and its relationship with ecosystems. It is highly relevant for researchers, managers and decision-makers in the field of water and environment. It provides up-to-date information on crucial factors and parameters that need to be considered when studying groundwater-ecosystem relationships in different environments worldwide.