This article focuses on irrigation and water use in a community in the Peruvian Andes, one of numerous villages in the region where these activities are carried out in an unusual way. The practices and principles that make up this tradition, defining the rights and duties of community members in making use of the resource most vital for life, are identified and evaluated based on comparative ethnographic research. It is argued that they provide a highly effective way of managing a scarce and fluctuating resource that is held in common, an older Andean tradition that may have been adopted by the Incas and endorsed as an official policy-all of which might help to account for its wide distribution in the region today. In this particular case, the principles help to create an extraordinary kind of community, a transparent and equitable one in which a basic material symmetry or proportionality is expressed at many levels. This symmetry is closely related to other basic commonalities among community members, but of particular interest are its effects on social solidarity and cooperation and its association with a strong sense of ethnic identity. The implications of this tradition for solving contemporary problems in water management are also briefly discussed, [sociocultural anthropology, irrigation, Andes, common-property] A nthropologists have long sought to understand the ways in which irrigation has shaped the development of societies in relatively arid parts of the world, beginning with Steward (1949Steward ( ,1955 and Wittfogel (1955Wittfogel ( , 1957. This interest reflects a broader fascination with the nature/ culture relationship-one of the great enduring themes, now understood to require a kind of ecological research that is historical and quite broad in scope (Biersack 1999;Kottak 1999), but still focused in some basic way on material relations. Yet the ethnographic study of irrigation began rather late, and, until recently, it did not appear to have taken us very far. The main thing learned during the early years was that hydraulic systems come in many shapes and sizes in various kinds of environments, so that, unless we narrow the field of inquiry and make some initial assumptions, few interesting generalizations can be made about them. The comparative study of these systems, which began in the 1960s but did not start to see significant advances until the 1980s (Hunt 1988;Kelly 1983), only reinforced this point of view.By limiting discussion in the simplest way, geographically, it becomes possible to make a few general statements about one major region of study, the Andes of Peru: (1) a distinctive kind of watering system was constructed there in prehistoric times-small-scale, vertically oriented canal systems, typically fed by alpine springs; (2) this was the only kind that could be built in most areas, due to limitations imposed by the topography and climate (Trawick 1994a:35-36); and (3) these small systems have, throughout history, formed the basis of a certain type of society, a village society...