This chapter draws on experiences and lessons learned from a process of hands-on, reflective game co-designing. The case is from the Urban Transition Öresund project (2013-14) which involved co-design and urban researchers, professional game designers, and civil servants working with complex, cross-sector sustainable urban planning in threemunicipalities in Scandinavia. The process included framing, co-designing, testing and playing what came to be called the “Urban Transition” game – explored in various real-world urban planning processes. By dissecting four co-design and play testing situations of this serious, dialogue game, the chapter aims to elucidate the inherent abilities of games as formats for collaboration, negotiation and mutual learning. The main claim is that games are practically “political” – in the sense that they can re-open taken-for-granted urban planning themes by emphasizing details and holistic views; can reveal assumptions about others by actualizing conflicts and can challenge current and possible future municipal, situated socio-material collaborative practices. Therefore, in urban planning processes[F1]  aimed at sustainable development, games and game co-designing should not be seen as de-politicized quick fixes but rather as highly “political” platforms for negotiation.