Transformations this century in communal irrigation in the Chiang Mai Valley, northern Thailand, are examined under the impact of political and economic changes such as state centralization, the intensification of capitalist agriculture, and urbanization. An anthropological political economy perspective is applied in placing anthropological subjects (irrigation weir communities and their leaders) at the intersection of local, national and global processes which allows scope for the agency of these subjects within the structural constraints imposed by political economy changes.