Water is one of the most widely shared resources on the planet, and the most vital for human survival after oxygen. It has a capacity to unite people that share a source of water, or to incite conflict among them as they compete for it. This systematic and thorough compilation of the available historical record of the very many treaties and agreements concluded in regard to the water resources of rivers and lakes shared across international borders offers fresh, compelling testimony to water being an agent of cooperation rather than of conflict. Moreover, the thematic maps featured in the Atlas help understand why this is so, and add new perspective to that of the legal records which make up most of the Atlas.