In recent years, supplemental irrigation systems have been used to boost production in rain-scarce agricultural areas. This report offers a guide to some technologies developed under A.I.D. auspices to help small farmers maximize the use of scarce water resources. The subject of rain fed agriculture is expressly stated as beyond the scope of the guide. Individual chapters, illustrated with photographs and drawings, are devoted to: (1) crop water requirements; (2) land grading for water control; (3) irrigation methods; (4) water quality and crop production; (5) drainage; (6) water measurement and distribution systems; (7) watercourse management; and (8) irrigation water supply. Efficient irrigation starts by knowing how much water a certain crop will use and how much water should be applied at each irrigation. Unfortunately, the amount of water actually reaching crops is only a fraction of the water originally delivered to a system. The reasons are many: evaporation losses, seepage, poorly designed and maintained ditches and fields, and useless vegetation growing in or along systems. For example, the surface of irrigated fields must be even and flat so that water will be equally distributed. The planting of annual crops the first year in newly graded fields is encouraged. Farmers must also choose methods of irrigation - surface, oversurface, or subsurface - that will: maintain a continuous supply of readily available moisture and a healthy soil environment for root systems; function properly under given soil and land conditions; and provide a satisfactory net return to the farmer. Three common irrigation problems are salinity, alkalinity, and waterlogging. Water, however pure, contains dissolved salts, and long-term application can result in significant salt accumulation in the soil. The preferred cure is to apply 10% more water than plants need, causing salts to be leached below the root zone. Excess water applications, however, can cause waterlogging, requiring construction of a drainage network. When measurements of water flow reveal large water losses, intensive rehabilitation must begin. Appendices include a glossary list of terms, a selected 33-item annotated bibliography of AID-sponsored research (1972-82), and a 12-item reference list (1953-77).