QCD PHASES AT HIGH-DENSITY AND INSTANTONS

The talk is an introduction into diquark condensation phenomena which occur in QCD at high energy density. They are driven by instantons and instanton-antiinstanton pairs (or ''molecules''), which generate attr action in some qq channels. A number of phases is possible, with or wi thout restoration of chiral symmetry: the work is not finished and we do not yet know which take place in real QCD. We also emphasize that s pecific diquark correlations play a significant role in baryon structu re, in particular making that of a nucleon very different of a Delta ( or other member of a decuplet). This ''small N-c'' scenario based on c omparison to QCD with two colors is contrasted with the ''large N-c'' one.