This chapter draws on experiences and lessons learned from a process of hands-on, reflective game co-design process. The case study was a part of the Urban Transition Öresund project (2012–14) which involved urban researchers, professional game designers, and civil servants working with complex, cross-sector urban planning tasks in four municipalities in Scandinavia. The process included framing, co-designing, testing, and playing the ‘Urban Transition’ game – explored in various real-world urban planning processes focusing on sustainable development. By analyzing four co-design and play-testing situations from the game co-designing process, the chapter aims to elaborate on games as formats for collaboration, negotiation, and mutual learning. The central claim is that games are political – in the sense that they can re-open taken-for-granted urban planning themes by drawing attention to value foundations and rules; can reveal assumptions about others by actualizing tensions and conflicts; and can challenge current and future municipal practices by highlighting situated, socio-material and collaborative interactions. Therefore, in urban planning processes aimed at sustainable development, games and game co-designing should not be seen as de-politicized quick fixes but rather as political platforms for challenging yet vital negotiation.