Scarcity of annual rainfall is the main cause of poverty in Spain. Onethird of the country, 182,000 square kilometres, has a mean annual rainfall between 300 and 500 millimetres and there are 35,000 square kilometres of steppe, 7 per cent. of the total area. Under such conditions the average labour return on cultivated land is small and fluctuations in crop production follow closely the high variability of precipitation. Poor returns and an unstable economy contribute to the poverty of the peasant farmer. It follows therefore that the fundamental object of Spanish national plans has been to raise the standard of living by overcoming the insufHciency of rainfall. Agrarian pro? blems in Spain have thus an environmental background; they are emphasized by their political repercussions. These problems can be diagnosed geographically from two aspects; the monocultural nature of Spanish agriculture and, associated with it, an excess of rural population and a seasonal unemployment of labour. To estimate the value of irrigation projects in the development of the country, it is therefore desirable to consider their relevance to agrarian problems, their value in the existing economy, and the progress that has been made in irrigation schemes during the present century.