Participatory research actively engages participants in some or all stages of the research process -- from deciding on scope and problem statement to actively collecting data to disseminating results and effecting change. Considering the shifting roles of participants and researchers in participatory ageing research, to the academic, participatory research becomes a venture into project and people management, local politics, consultancy and community building. First, we present a literature overview of the promises and pitfalls of participatory research. Then, drawing on a university initiated participatory study involving older people as co-researchers in a neighbourhood in Groningen, the Netherlands, we discuss the shifting roles and expectations of all of those involved in the participatory research process. We conclude that a central question that requires continuous negotiation in the participatory research process is: what's in in for whom?