While participatory design crosses the boundaries between technology production and use, it does not erase them. In accounts of participatory projects, the work of negotiating and changing these boundaries often recedes into the background, yet it is crucial in shaping the very nature and scope of what is achievable. In this paper, we report on our various experiences of ‘boundary crossing’ in four very different participatory design contexts. We argue that in each setting a key task consists of enlisting the effort, imagination, trust and commitment of users, and the sharing of risks and responsibilities. We compare and discuss the different strategies, methods we have devised to achieve this within the local politics of each setting.