Increasingly, metropolitan planning is challenged by the tensions between the search to become a competitive metropolis' as well as a 'sustainable metropolis'. Many urban regions struggle with dealing with these complexities on the metropolitan level and try to find bottom-up solutions to balance between the supposed merits of new territorial frames and identities on the metropolitan level and the often local political spaces. Yet, the political strength of metropolitan areas, necessary to design and implement these policies, remains rather weak. The overarching purpose of this special issue is to develop a more robust and rigorous definition of what 'thinking metropolitan' means, particularly for five medium-sized city-regions of the early twenty-first century.