In the European context, cities and regions play a key role in boosting circularity and achieve the European Green Deal action plan ambition to ‘boost the efficient use of resources by moving to a clean, circular economy’. To this end, cities and regions will be instrumental in promoting circularity through engagement with key actors and integration of circular economy (CE) goals within their policies and spatial plans. To support this effort, it is essential to develop appropriate metrics and tools for evaluating the progress and transition towards a circular economy. Although numerous new assessment methodologies have been suggested (Corona et al., 2019), they generally focus on quantitatively assessing how circular a project, system, or business is, or on evaluating the extent to which circular strategies align with the principles of a circular economy. Current metrics rarely extend beyond material sustainability assessments, which means they often do not capture the complexity of the CE transition and lack a comprehensive, integrated perspective. In particular, what they omit are the spatial (Williams, 2020), the governance (Korhonen et al., 2018) and the social dimensions (Pitkänen et al., 2020). In this paper, we propose a holistic transition assessment tool developed and tested across several metropolitan regions, including Amsterdam, Naples, Łódź, Hamburg and Pécs, being at different stages of the circular economy transition. The final version of the tool was applied in two cases, the Amsterdam Metropolitan Area and the city of Tomaszów Mazowiecki. The tool focuses on five dimensions: (1) governance structures, (2) awareness, comprehensiveness of the sustainability assessment, (3) tools for measuring material stocks and flows as well as (4) for co-creation of solutions and strategies with stakeholders, and (5) circular built environment. The results of applying the tool in a series of workshops with regional CE stakeholders allow for exploring the following questions: What is the state of the transition towards CE in European urban regions from a holistic perspective? What hinders these transitions? And how to identify means to overcome those barriers? The assessment tool is of interest for regional and urban policy-makers, planners and stakeholders engaged in development of CE strategies and policies. What is more, the results presented in the paper allow for comparative insights into the state of transition towards CE and for drawing lessons on what it takes to nudge the development of regions and cities towards circularity.