The report examines governmental capacity building to support the development and effective implementation of a sustainable mobility transition agenda across the 6 Sump Plus cities. More precisely, it seeks to understand when, why and how sustainable urban planning emerged as an urban public policy issue, what priorities are set and by whom. The main assumption is that policy capacities and their instrumental uses across levels and over time play a critical role in city governments’ ability to overcome these barriers and intensify the pace and scope of sustainable transitions. Drawing on public policy research, urban studies and comparative politics, the report builds on previous work done on historical transport policy developments and policy capacities to support urban sustainable mobility transitions in a multi-level governance context . It introduces the analytical framework used in order to analyze governmental capacity building across the 6 Sump Plus cities. Beyond the classic approach to governance, it proposes a broader conception of the term to include the whole set of vertical and horizontal relationships in sustainable urban transitions, as well as the different types of policy capacities needed to govern sustainable urban mobility transitions at different policy stages.