It is more than 35 years ago that the first heavy-ion collisions occurred at CERN and in the meanwhile an exploratory field has grown into a precision era.
The seminar will give a review of studies of the high-density regime of the QCD phase diagram with heavy-ion and proton beams. The nature of the Quark-Gluon Plasma, the onset of its production as well as the transition to hadrons will be discussed. A set of observables will be introduced which allow one to understand the key properties of the Quark-Gluon Plasma.
Finally, measurements relevant to astroparticle physics will be discussed.