This chapter discusses how shifting the focus from rather homogeneous socio-technical systems to cities as heterogeneous arenas for sustainability transitions may help us address some of these problems. Not only is such an arena located at the intersection of various types of socio-technical regimes and emerging niches, but also cities are 'hotspots' for socio-economic and socio-political changes. Such a perspective thus rather emphasizes the inherent partiality of transition approaches, the importance of bottom-up or 'inside-out' processes of sense-making about transitions, and their dependence on other social and political dynamics. The chapter applies a bottom-up perspective of 'transitions in the making' and 'cities as contested arenas' for such processes of change to two exemplary case studies in Graz, Austria, and Freiburg, Germany. It gives a short introduction to conceptual approaches to understand socio-technical transitions and recent conceptual developments emphasising the role of space, and conflictual character of transitions in the making.