There is increasing interest in student retention in open and distance learning. This article looks at the role of proactive interventions from the institution to its students and discusses concepts such as the maximum possible increases in retention and issues such as who to target for intervention, the different types of retention possible and which media to use. It surveys the evidence for the effectiveness of such interventions both in and outside the UK Open University (UKOU) and concludes that in the case of the UKOU there are clear financial benefits to the institution, the individual and the UKOU's funding agency, the UK Government.