This book represents the proceedings of a symposium held during the centennial meeting of the American Physical Society. It covers the latest results in experimental heavy ion physics from the Alternating Gradient Accelerator in the US and the SpS at CERN, and summarizes the current theoretical and experimental state of the field before the commissioning of RHIC. Among the highlights are the theoretical predictions made for what the experimentalists will see in the high temperature matter expected to be formed at the new machine.