City-regions as sites of sustainability transitions have remained under-explored so far. With our comparative analysis of five diverse European city-regions, we offer new insights on contemporary sustainability transitions at the urban level. In a similar vein, the pre-development and the take-off phase of sustainability transitions have been studied in depth while the acceleration phase remains a research gap. We address this research gap by exploring how transitions can move beyond the seeding of alternative experiments and the activation of civil society initiatives. This raises the question of what commonalities and differences can be found between urban sustainability transitions. In our explorative study, we employ a newly developed framework of the acceleration mechanisms of sustainability transitions. We offer new insights on the multi-phase model of sustainability transitions. Our findings illustrate that there are no clear demarcations between the phases of transitions. From the perspective of city-regions, we rather found dynamics of acceleration, deceleration, and stagnation to unfold in parallel. We observed several transitions—transitions towards both sustainability and un-sustainability—to co-evolve. This suggests that the politics of persistence—the inertia and path dependencies of un-sustainability—should be considered in the study of urban sustainability transitions.

The recent literature on intermediaries in urban sustainability transitions has studied their role as a translator between innovative niches and incumbent regimes. In urban sustainability transitions, intermediaries from both civil society and public institutions seek to bridge diverging world views and communicate innovative lessons learned back to the incumbent regime. How these intermediaries are embedded in local governance contexts and how the political dynamics inherent to urban sustainability transitions play out remains a research gap. As these transitions require political consensus-building, we explore the interaction between Transition Town Initiatives (TTIs) as niche intermediaries seeking to transform society from below, and regime-based transition intermediaries operating from above. In a comparative study of four German cities, we analyse why and how niche and regime intermediaries build partnerships for urban transitions towards sustainability. While Transition Town Hannover and Bluepingu in Nuremberg have successfully established partnerships with the municipalities, Transition Town Göttingen and Transition Town Kassel have struggled in their efforts to do so. These differences can be explained by the interactions between structural conditions, political priorities and institution-building, as well as the proficiency of transition intermediaries.

Throughout Europe, planners and policymakers are trying to make use of the potentials of polycentric development on a regional scale by creating polycentric metropolitan regions. Only a few of these regions have achieved the stage of implementation. The Saxon Triangle is a polycentric metropolitan region located in the Eastern part of Germany. Common governance structures as well as shared decision-making have already been built up since 2002. This article outlines the changes that are ongoing in the debate about city-regions in Germany since the 1990s. Then it traces the emergence and implementation of the Saxon Triangle. Based on an analysis of the collective decision-making procedures in the Saxon Triangle, conclusions will be drawn regarding the question whether polycentric metropolitan regions can fulfil their expected role of building blocks in metropolitan Europe. Emphasis is placed on an actor-oriented perspective on polycentricity.

Das Bundesministerium für Wissenschaft und Klimaschutz (BMWK) möchte innovationsfreundliche Rahmenbedingungen für Reallabore schaffen. Im Sommer 2023 hat es dazu ein Grünbuch Reallabore veröffentlicht und einen Konsultationsprozess für ein Reallabore-Gesetz eingeleitet. Das Netzwerk Reallabore der Nachhaltigkeit begrüßt die Initiative, sieht aber zugleich erheblichen Gestaltungsbedarf. Die NaWis-Mitglieder unterstützen die hier vorgestellte Position des Netzwerks.