This volume constitutes the Proceedings of a Europhysics Study Conference held in Erice, Sicily from March 17 to 24, 1980. The objective of the meeting was to bring together practitioners of two different approaches to the unification of the fundamental par ticle interactions: supersymmetry and supergravity on the one hand, and grand unified gauge theories on the other hand. The hope was that exposure to each others' ideas and problems would at least aid mutual comprehension, and might start people thinking how to develop a synthesis of the two approaches which could avoid their individual...