The problem of the arid zones can be summed by the following comparison: whereas cultivated land represents barely one-tenth of the land surface of the globe, the arid and semi-arid areas cover more than one-third. In other words for each acre of cultivated land there are three or four acres that are practically unused by man because they are desert or covered with sparse vegetation. The countries where the problems of arid lands development is most acute are usually those with the poorest scientific and economic resources. UNESCO is required under its constitution to promote scientific research in order to improve man's leaving conditions.