The basic ideas which motivated the search for a deconfinement phase transition in high energy nucleus--nucleus collisions are reviewed. The main results obtained within the energy scan programme at the CERN SPS are presented. Several anomalies in energy dependence of hadron production predicted as signals of deconfinement phase transition are observed and they indicate that the onset of deconfinement phase transition is located at about 30 A GeV. For the first time we seem to have clear evidence for the existence of a deconfined state of matter in nature.

PACS numbers: 24.85.+p