This book presents a unique and up-to-date summary of what is known about groundwater on our planet, from a global perspective and in terms of area-specific factual information. Unlike most textbooks on groundwater, it does not deal with theoretical principles, but rather with the overall picture that emerges as a result of countless observations, studies and other activities related to groundwater in all parts of the world. The focus is on showing the role and geographical diversity of groundwater—a natural resource of great importance in daily life, but poorly understood by the general public and even by many water sector professionals. The book starts by analysing groundwater in the context of the hydrological cycle. Subsequently, groundwater systems as physical units, with their boundaries mainly defined by geological conditions, are reviewed. The next chapter looks at groundwater as a resource, paying attention, among others, to its quantity and quality, to the differentiation between renewable and non-renewable resources, and to the techniques for withdrawing groundwater. This is followed by a systematic documentation of the quantities of groundwater withdrawn and used around the world, and of the corresponding shares of groundwater in each of the main water use sectors. After that, steadily growing needs for groundwater management interventions are identified, resulting from local human activities and global change (including demography, economic development and climate change). Finally, groundwater resources management is addressed and real-life cases are described that illustrate actions taken and experiences with different issues in different parts of the world. The authors attempted to write this book in such a way that it is accessible to a wider readership than just groundwater professionals. It will also benefit non-groundwater specialists who work in groundwater-related fields (water managers, land use planners, environmentalists, agronomists, engineers, economists, lawyers, and journalists), by broadening their understanding of groundwater and making them aware of the huge variety of groundwater settings. Groundwater specialists will use the book as a convenient reference on the geographical diversity of groundwater. Part of the contents or interpretations offered may even be new to them or enhance their knowledge of some aspects. The many maps, tables, and references will save much time for those who would otherwise have to search elsewhere for basic information on the globe’s groundwater.