INSTANTONS IN QCD

The authors review the theory and phenomenology of instantons in quant um chromodynamics (QCD). After a general overview, they provide a peda gogical introduction to semiclassical methods in quantum mechanics and held theory. The main part of the review summarizes our understanding . of the instanton liquid in QCD and the role of instantons in generat ing the spectrum of light hadrons. The authors also discuss properties of instantons at finite temperature and how instantons can provide a mechanism for the chiral phase transition. They give an overview of th e role of instantons in some other models, in particular low-dimension al sigma models, electroweak theory, and supersymmetric QCD.