Background: Peer support interventions involve people drawing on shared personal experience to help one another improve their physical or mental health, or reduce social isolation. If effective, they may also lessen the demand on health and social care services, reducing costs. However, the design and delivery of peer support varies greatly, from the targeted problem or need, the setting and mode of delivery, to the number and content of sessions. Robust evidence is essential for policymakers commissioning peer support and practitioners delivering services in health care and community settings. This map draws together evidence on different types of peer support to support the design and delivery of interventions.Objectives: The aim of this map was to provide an overview of the volume, diversity and nature of recent, high quality evidence on the effectiveness and costeffectiveness of the use of peer support in health and social care. Search Methods: We searched MEDLINE, seven further bibliographic databases, and Epistemonikos for systematic reviews (in October 2020), randomised controlled trials (in March 2021) and economic evaluations (in May 2021) on the effectiveness of peer support interventions in health and social care. We also conducted searches of Google Scholar, two trial registers, PROSPERO, and completed citation chasing on included studies.Selection Criteria: Systematic reviews, randomised controlled trials and economic evaluations were included in the map. Included studies focused on adult populations with a defined health or social care need, were conducted in high-income countries, and published since 2015. Any measure of effectiveness was included, as was any form of peer support providing the peer had shared experience with the participant and a formalised role.