This book explains the emergence of a profoundly new understanding of the fundamental forces of Nature.

Seven years after the first experiments in the new field of Nuclear Physics, the Highly Relativistic Heavy Ion Physics, the Nato-Advanced- Study-Institute on the 'Particle Production in Highly Excited Matter' was held from July 12 till July 24, 1992, at Il Ciocco, Castelvecchio Pascoli, near Lucca in Italy. The school took place at a mo ment when intensive efforts are mounted by the scientific community of Relativistic Heavy Ion Physics to meet the extraordinary challenge of the new upcoming physics opportunities. The gold beams of 10 GeV A at Brookhaven AGS have been sent to the experiments this Summer and we extent our congratulations to the persons and teams who made this possible. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven is under construction and expected to allow experiments to see collisions in the intersec tion regions early 1998. The lead beams at the SPS at CERN scheduled for summer 1994 are eagerly awaited by 6 large experiments, and many scientists are planning the experiments at the planned LHC with heavy ions to be turned on before the year 2000. Seen against this background of rather fierce activity, we were most delighted when NATO accepted our application for an Advanced Study Institute oriented to the main subject of this young and dynamic field of research. We are very grateful to the Scientific Affairs Division of NATO and Dr. L. DaCunha, the director of the Advanced Study Institute program for giving our community this opportunity.