These UNDP-World Bank guidelines summarize information on the reuse of wastewater for irrigation. They integrate the World Health Organization health guidelines for the reuse of wastewater with the Food and Agriculture Organization of the United Nations water quality guidelines for irrigation. The report also summarizes relevant agronomic information including potential benefits of wastewater reuse and its environmental implications. Properly designed, adequately implemented wastewater reuse is an environmental protection measure that is superior to discharging treated wastewater into surface waters. Wastewater reuse could also free large amounts of fresh water currently used for irrigation and make this resource available to meet the growing needs for fresh water of cities and towns in developing countries. The guidelines suggest consideration of land application as a disposal option even where no urgent need for additional sources of irrigation water exists. Close collaboration between the sectors involved - agriculture, water and wastes, environmental protection, and health - is essential, and this collaboration raises a number of institutional issues reviewed in these guidelines. Finally, the report provides guidance for choosing among technical and policy options, and it proposes a framework for inclusion of economic and financial considerations. The guidelines will help task managers and development agency staff to prepare wastewater reuse projects. Water quality and quantity problems at the urban-rural interface are increasing throughout the developing world. It is the authors ' hope that this report will facilitate the consideration of reuse as an integral part of water management strategies in development projects.