The possibilities and productivity of farmer participation will be conditioned by the situation in which water users find themselves. The incentives and constraints they face derive from many sources, including three broad categories of most important factors: historical factors, physical and economic factors, and socio-cultured and political factors. The knowledge and skills which water users can bring to the tasks of management, as well as their disposition to accept responsibility, will depend a great deed on the origins of each irrigation system. Physical and economic factors might appear to correspond respectively to the factors which affect supply of and demand for irrigation water. These factors are important because of the observation that farmers' investment of time and effort in irrigation management activities reflects their need for adequate and reliable water. Ethnic and social differences can form lines of cleavage and potential conflict among water users, especially if these correspond to differences in land tenure status or in access to water.