This volume in the series Ecological Bulletins deals with the ecological and social problems of desert encroachment. It puts man and his activities into an ecological con- text and outlines the causes of desert encroachment and remedies which can be used. The report has been prepared in close cooperation between UNEP and SIES as a background document for the 1977 UN Conference on Desertization. It is also a furth-er step in the efforts of the Editorial Board of the Ecological Bulletins to publish re-ports which are relevant to the present discussions on important environmental issues.