INSTANTONS IN QCD VACUUM AND PHASE-TRANSITIONS

In this lecture we review recent development in non-perturbative QCD r elated to instantons. The ''instanton liquid model'' was shown to repr oduce not only the basic vacuum parameters (the condensates) but even hadronic correlators. New phenomenological information obtained from l attice simulations also confirm it. Meanwhile the model itself was dev eloped into a self-consistent approach, allowing in practice keep 't H ooft interaction to all orders and also was generalized to non-zero te mperatures and high densities. In both case chiral restoration phase t ransition is a structural transition from a relatively random instanto n liquid to a gas of a strongly correlated instanton-anti-instantons, at finite T they are pairs (or ''molecules'') and at high density they are ''polymers'', or bound diquarks.