Irrigation has long been of interest in the study of the past. Many early civilizations were located in river valleys, and irrigation was of great economic importance for many early states because of the key role it played in producing an agricultural surplus, which was the main source of wealth and the basis of political power for the elites who controlled it. Agricultural surplus was also necessary to maintain the very features of statehood, such as urbanism, full-time labor specialization, state institutions, and status hierarchy. Yet, the presence of large-scale or complex irrigation systems does not necessarily mean that they were under centralized control. While some early states organized the construction, operation, and maintenance of irrigation works and resolved conflicts related to water distribution, other early governments left most of the management to local farmers and controlled only the surplus. The cross-cultural studies in this volume reexamine the role of irrigation in early states. Ranging geographically from South America and the southwestern United States to North Africa, the Middle East, and Asia, they describe the physical attributes and environments of early irrigation systems; various methods for empirical investigation of ancient irrigation; and irrigation''s economic, sociopolitical, and cosmological dimensions. Through their interdisciplinary perspectives, the authors-all experts in the field of irrigation studies-advance both methodological and theoretical approaches to understanding irrigation in early civilizations.