Renormalons

A certain pattern of divergence of perturbative expansions in quantum field theories, related to their small and large momentum behaviour, is known as renormalons. We review formal and phenomenological aspects of renormalon d ivergence. We first summarize what is known about ultraviolet and infrared renormalons from an analysis of Feynman diagrams. Because infrared renormal ons probe large distances, they are closely connected with non-perturbative power corrections in asymptotically free theories such as QCD. We discuss this aspect of the renormalon phenomenon :in various contexts, and in parti cular the successes and failures of renormalon-inspired models of power cor rections to hard processes in QCD, (C) 1999 Elsevier Science B.V. All right s reserved.