Growing scarcity of freshwater worldwide brings to light the need for sound water resource modeling and policy analysis. While a solid foundation has been established for many specific water management problems, combining those methods and principles in a unified framework remains an ongoing challenge. This Handbook aims to expand the scope of efficient water use to include allocation of sources and quantities across uses and time, as well as integrating demand-management with supply-side substitutes. Socially efficient water use does not generally coincide with private decisions in the real...