For many years, debates concerning arid lands development have focused on the problems of salt accumulation and soil damage from past irrigation activities. Today, discussions of global arid lands issues turn to the current problems of land degradation in Africa. That continent, two-thirds of which is arid, semiarid or subhumid, embodies more than any other the difficulties of arid lands development. Such difficulties stem from the physical and biological constraints imposed by nature such as inadequate water, thin soils and sparse vegetation. They also stem from man's failure to develop plans and projects that work within these constraints. The ecosystems that exist in such climates are fragile, and subtle changes in the balance of the system can lead to rapid degradation of the resource base.