There are 1.8 billion young people in the world today. If engaged effectively, youth are resources and agents of change in their communities. Involving youth in work that impacts their communities has positive outcomes for youth wellbeing; and for their communities. But, youth are often marginalized, particularly in humanitarian settings. Youth wellbeing is linked to seven key protective factors: positive emotions, hope, relationships, meaning, accomplishments, autonomy, and engagement. Understanding protective factors as potential mechanisms for intervention-related change in wellbeing is a priority for research in humanitarian settings. If youth are to be meaningfully engaged as intervention agents, their work should focus on a community need. Humanitarian crises increase mental health disorders; and `normal' distress and psychological reactions affect a large percentage of the population. Yet, human resources for health are often insufficient to meet needs. Understanding the capacities of youth to support communities in the context of disasters has been noted as a research imperative. Globally, task-sharing interventions train non-professional lay community members to provide mental health care. As one example, Problem Management Plus (PM+) trains community mental health workers (CMHW) and is effective in humanitarian settings for common mental disorders and for mental distress and other problems that emerge in response to crises. We propose to engage youth – aged 18-24 years, as youth CMHW, to implement PM+ with at-risk adults (18+ years) in their communities. The Syrian refugee crises, one of the worst humanitarian crises in recent history, provides a relevant setting to implement this project. Lebanon hosts ~1.5 million Syrian refugees, and about 60% of Syrian refugees aged 15-24 years are not employed, and not in school. The Specific Aims are: Aim 1: Assess the effectiveness of being a Y-CMHW on their wellbeing, resilience, and stress levels; as compared to an equivalent control group (ECG) of Syrian refugee peers. Aim 2: Identify the mechanisms associated with changes in wellbeing, resilience, and stress. Our conceptual model describes links between the intervention, the mechanisms, and outcomes. Aim 3: Evaluate the feasibility, acceptability and fidelity of Syrian refugee youth as CMHW implementing PM+ with clients using RE-AIM as a framework for collecting implementation data. A community-engaged research approach will involve community members, including youth, in all aspects of the research project. Our results will (a) elucidate critical mechanisms through which engagement of youth to support their community enhances their own wellbeing; (b) inform research around humanitarian/refugee settings, mental health, and Y-CMHW interventions; and (c) provide a robust basis for a follow-up study via a larger RCT. Though we assess the impact of Y- CMHW in the Syrian refugee context, the premise of this intervention and its findings are equall...