Background: Although mutual support and self-help groups based on shared experience play a large part in recovery, the employment of peer support workers (PSWs) in mental health services is a recent development. However, peer support has been implemented outside the UK and is showing great promise in facilitating recovery. Aims. This article aims to review the literature on PSWs employed in mental health services to provide a description of the development, impact and challenges presented by the employment of PSWs and to inform implementation in the UK. Method.An inclusive search of published and grey literature was undertaken to identify all studies of intentional peer support in mental health services. Articles were summarized and findings analyzed. Results. The literature demonstrates that PSWs can lead to a reduction in admissions among those with whom they work. Additionally, associated improvements have been reported on numerous issues that can impact on the lives of people with mental health problems. Conclusion. PSWs have the potential to drive through recovery-focused changes in services. However, many challenges are involved in the development of peer support. Careful training, supervision and management of all involved are required.