This book originated in the Workshop on "Hadronic Matter at Extreme Energy Density," held at the Ettore Majorana Center in Erice, October 13-21, 1978. The lectures have been expanded to their present size, and the contributions of seven seminars have been represented by abstracts which should stimulate the reader's interest and guide him to the original literature. The title of the book perhaps does not fully represent its content but still is a good indication of the conceptual motiva­ tion of our Workshop. The development of physics in recent years has filled in the first details of the grand design which was initiated with the theory of general relativity and aspires to a synthesis of all the different interactions. However, this development has not been a linear one but .has followed a divided pattern: general relativity had its phenomenological domain in cosmology and had little to do with high-energy elementary particle physics. It was progress in the knowledge of symmetries in particle physics that fueled the advance toward the present formulation of supergravity, thus help­ ing to heal this historical separation. The great program would not have advanced so far if our attention had all the time stayed focused at infinity, where the great issues are.