This introductory chapter discusses the importance of water to humans, its growing scarcity relative to human populations, and, consequently, the increasing potential for water-related conflicts between States. Humans are straining the limits of a resource essential to their survival. Moreover, humans are capable of altering natural conditions to the point that their neighbors are deprived of fresh water they need and have historically relied upon. While international law plays an important role in resolving conflicts between states, it can play an even more valuable role in preventing them, in establishing conditions that are conducive to cooperation among states sharing freshwater resources. Indeed, cooperation is itself a logical outgrowth of rules of international law applicable in this field.