In several low- and middle-income countries (LMICs), peer facilitators, defined as adolescents or young adults selected from the group or community they serve, are employed to work in communities and schools as part of national and non-governmental adolescent health programmes. There are several reasons for this. Training lay peer facilitators to deliver adolescent health interventions can increase capacity for scaling up and be more cost-effective than working with specialised staff. Peer facilitators may also be better able to communicate with adolescents than older adults, and perceived as a more credible source of information. Peer facilitators might have better access to marginalised groups who have limited engagement with existing health programmes. Critically, empowering young people to inform and implement adolescent health programmes should make these more relevant and effective. The selection, training, supervision and incentivisation of peer facilitators are all deemed critical to success and sustainability. Peer-facilitated community-based interventions show promise to improve mental health and reduce violence and substance use in LMICs, though further robust studies are needed to strengthen the evidence base.