Irrigation development investments are designed to increase food supply and rural income and to improve the quality of life for the rural poor. Yet many irrigation projects have had poor agronomic and economic results as well as unintended and undesirable social effects. Due to inappropriate project design and a failure to fully consider sociological factors, projects are often characterized by water use inefficiency, poor maintenance, and deviance. This article identifies social factors that have facilitated project success. Cases are used to exemplify key lessons that have emerged from field experience. Emphasis is given to unintended project outcomes, farmer participation, site‐specific design, and the match of irrigation organizational design to the type of technology.