Limits of Confinement: The First 15 Years of Ultra-Relativistic Heavy Ion Studies

The study of high energy nuclear collisions has entered a new stage with RHIC; it therefore seems a good time to ask what we have learned from the experimental results obtained up to now. I recall what we had expected to find when the SPS and AGS programs were started, summarize what actually was found, and then try to assess what we have learned from the results.