This chapter explains how and why urban sustainability transitions different from other types of transitions, and how urban transitions unfold over time and space. It discusses these questions through two case studies: one is the Carlsberg City District urban development project in the City of Copenhagen; the other is the Cycle Superhighways project, coordinated by an independent secretariat and developed with the involvement of various municipalities from the Greater Copenhagen area, the regional authority and the Danish Road Directorate. The way in which the chapter addresses the research questions is based on Arenas of Development Theory (AoD). One of the basic principles of this theory is that no single actor in a transition process has complete knowledge of what is happening. The development of Carlsberg City District was initiated in 2006, as the brewery production was relocated, leaving behind an area of 33 hectares to be developed for commercial and residential use.