Many of the earth's arid and semiarid zones are used primarily for pastoral production which, particularly in the Third World, takes the form of traditional nomadic or transhumant systems based on common rangelands. Efforts made to date to improve management in these systems have been conspicuously unsuccessful because the interventions attempted have been perceived as inappropriate by the pastoral producers themselves, and thus have not been adopted. It has become evident that development interventions must be based on existing management systems if they are to be accepted and self-sustaining.