Illicit drug use in prison is highly prevalent and brings with it health risks for the prison population like HIV, Hepatitis B and C and tuberculosis. Studies show that harm reduction (HR) measures, such as Opioid Substitution Treatment and Needle and Syringe Programs, are effective in reducing harm both in and outside of prisons. However, HR in prison is still not up to par, despite prisoners’ positive attitudes to some HR initiatives. Nor it is always clear what HR means to them, as prisoners have hardly ever been asked. Prisoners are rarely involved in the development and implementation of in-prison HR strategies and when they are, the level of participation never exceeds consultation. As these HR strategies directly affect prisoners, it is essential to involve them in the development and implementation of these strategies. To counter this lack of involvement of the target group, we are using the method of Participatory Action Research (PAR). The central goals of this research are twofold: (1) using the method of PAR we intend to provide a richer conceptualization of HR that takes into account prisoners’ views and (2) we want to research how PAR as a methodological approach can contribute to a more substantial form of participation in a prison context. Arnstein’s ladder of citizen participation is used to operationalise prisoner participation and, applied to prisoners, consists of five levels: informing, consulting, involving, collaborating, and devoting and empowering.