Quality, outcomes and cost-effectiveness of methods of teaching and learning in colleges and universities are being scrutinised more closely. The increasing use of peer tutoring in this context necessitates a clear definition and typology, which are outlined. The theoretical advantages of peer tutoring are discussed and the research on peer tutoring in schools briefly considered. The substantial existing research on the effectiveness of the many different types and formats of peer tutoring within colleges and universities is then reviewed. Much is already known about the effectiveness of some types of peer tutoring and this merits wider dissemination to practitioners. Directions for future research are indicated.