It is estimated that desertification affects about one-sixth of the world’s population and 70% of all drylands, amounting to 3.6 billion hectares, or one quarter of the total land area of the world. As defined by the United Nations Convention to Combat Desertification (UNCCD), desertification means land degradation in arid, semi-arid and dry sub-humid areas that results from various factors, including climatic variations and human activities. The reduction or loss of the biological or economic productivity of rainfed or irrigated croplands, ranges, pastures and woodlands in these climatic zones entails serious land degradation in terms of soil erosion, deterioration of the physical, chemical, biological and economic properties of soil, and long-term loss of natural vegetation. The contributions contained in this publication stem from an international seminar on desertification that was held in N’Djamena (Chad) from 30 October to 4 November 2000. Over 50 scientists from 14 countries addressed issues of desertification, particularly with regard to restoring degraded dryland areas, and the conservation and sustained management of freshwater resources in the world’s dry zones.