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...