This volume contains the greater part of the papers submitted to the High Energy Physics portion of the 1983 Orbis Scientiae, then dedicated to the eightieth year of Professor P. A. M. Dirac. Before the vol,ume could be published, Professor Dirac passed away on October 20, 1984, thereby changing the dedication of this volume, and its companion, on Information Processing in Biology, to his everlasting memory. Since 1969, Professor Dirac had given the opening address at each of these conferences. He was unable to prepare a manuscript of his last paper in 1983. His impact on science already has been enormous. The consequences of his thought and work for future developments are incalculable. Regrettably, Professor Dirac's last appearance at this series of conferences, begun in 1964 as the Coral Gables Conference on Symmetry Principles at High Energy, coincided with the twentieth, and the last of these. The work and expense involved in organizing them and preparing the proceedings have corne to far exceed the physical capabilities and the support received by the Center for Theoretical Studies for this program. The delayed appearance of these proceedings, for which the editors humbly apologize, is a manifestation of the inadequate support. On the other hand, the organizers and editors thank the many distinguished participants who, over the years, made these meetings exciting and productive arenas for the dissemination of ideas in high energy physics and related fields.