Participation has been linked with better health outcomes for young people in a range of settings, with an extensive literature extolling the benefits of a participatory approach to youth-focused HIV-prevention programs in particular. However the processes of participation, and how the ideals outlined in the participation literature can be achieved in the difficult circumstances in which many youth health promotion programs operate, are less often discussed. This thesis responds to calls for more nuanced documentation of situated participatory practices by developing a detailed and contextualised analysis of youth participation in a Photovoice project in the Highlands of Papua New Guinea. The analysis draws upon data generated over a ten-month period (photo-stories, individual interviews, written accounts of participation, group discussions, artefacts produced during participatory analysis, and field-notes) to describe how participation in a project of self-reflection and self-representation can support dialogical engagement and the demonstration of critical thinking. The thesis explores the relationship between these psycho-social changes and young people’s subsequent ability to enact strategies to improve their health and well-being. Findings challenge idealised representations of youth participation, demonstrating that young people’s ability to act is mediated and bounded by the health-related contexts in which they live. They also demonstrate a disconnect between youth health priorities and the priorities of the programs ‘targeting’ them; and point to the importance of HIV-prevention programs working to support ‘in-between’ spaces where youth and community leaders can connect in order to affect wider social environments. In providing a detailed examination of a Photovoice process, this thesis extends the theoretical basis of an increasingly popular participatory research tool. In analysing the relationship between young people’s participation in a research project and their ability to take action on health, this thesis also contributes to social psychological understandings of the pathways through which participation may impact upon health, and in particular affect efforts to prevent HIV.