This is the first book to treat the major examples of megadrought and societal collapse, from the late Pleistocene end of hunter–gatherer culture and origins of cultivation to the 15th century AD fall of the Khmer Empire capital at Angkor, and ranging from the Near East to South America. Previous enquiries have stressed the possible multiple and internal causes of collapse, such overpopulation, overexploitation of resources, warfare, and poor leadership and decision-making. In contrast, Megadrought and Collapse presents case studies of nine major episodes of societal collapse in which megadrought was the major and independent cause of societal collapse. In each case the most recent paleoclimatic evidence for megadroughts, multiple decades to multiple centuries in duration, is presented alongside the archaeological records for synchronous societal collapse. The megadrought data are derived from paleoclimate proxy sources (lake, marine, and glacial cores; speleothems, or cave stalagmites; and tree-rings) and are explained by researchers directly engaged in their analysis. Researchers directly responsible for them discuss the relevant current archaeological records. Two arguments are developed through these case studies. The first is that societal collapse in different time periods and regions and at levels of social complexity ranging from simple foragers to complex empires would not have occurred without megadrought. The second is that similar responses to megadrought extend across these historical episodes: societal collapse in the face of insurmountable climate change, abandonment of settlements and regions, and habitat tracking to sustainable agricultural landscapes. As we confront megadrought today, and in the likely future, Megadrought and Collapse brings together the latest contributions to our understanding of past societal responses to the crisis on an equally global and diverse scale.