This paper 1s a synthesis of studies in vanous irrigated areas in Spain. Agricultural development in large areas where major irrigation projects are carried out by the government is a complex problem. The change from dryland to wetland crops needs irrigation water, but many other factors are necessary for farmers to take advantage of all the possibilities irrigation can provide. The use of a new factor, according to the principle of the "package of practices," requires that simultaneously other factors be changed. One of the most important factors that determine the rate of adoption of irrigation is the increase in returns; the greater that increase, the greater the stimulus for change from dryland to wetland crops. Availability of credit to acquire the means of production needed for the intensification of crop farming is essential if farmers do not waste such funds. Another factor is the existence of marketing organizations, especially for marketing agricultural products. And the agranan structure of the zone has an influence on the process of irrigation adoption, especially the size of farms. Farmers' level of education, professional training, initiative, and dynamism, and the uncertainty mvolved in the change to wetland farmmg, whose techmcal and economic aspects are not famihar to farmers, have a great influence on irrigation adoption. The importance of these factors is manifest in the high rate of irrigat10n adoption 10 areas where some irrigated parcels existed pnor to the irrigation project