Peer interventions delivered for prisoners by prisoners offer a means to improve health and reduce risk factors for this population. The variety of peer programs poses challenges for synthesizing evidence. This article presents a typology developed as part of a systematic review of peer interventions in prison settings. Peer interventions are grouped into four modes: peer education, peer support, peer mentoring, and bridging roles, with the addition of a number of specific interventions identified through the review process. The article discusses the different modes of peer delivery with reference to a wider health promotion literature on the value of social influence and support. In conclusion, the typology offers a framework for developing the evidence base across a diverse field of practice in correctional health care.