This summary document, which is derived from a full technical report under the same title was prepared mainly by Paul Harrison. The full report is the product of cooperative work by most technical unts of FAO. It was prepared by a team led by Jelle Bruinsma under the general direction of Hartwig de Haen, Assistant Director-General, Economic and Social Department. Members of the core team were Nikos Alexandratos, Josef Schmidhuber, Gerold Bödeker and Maria-Grazia Ottaviani.