Groundwater has long been an object of intense scrutiny. Only recently have methods become available that permit ecologists, hydrologists, and environmental scientists to assess the biotic and abiotic status of these all-important aquifiers. This book reviews and synthesizes these emerging results by focusing attention on the dynamics of water movement through complex subterrranean ecosystems, the biological organization and the factors that constrain these ecosystems, alluvial and karst ecosystem functions, and contamination, management, and remediation.