In the last thirty years, European local authorities have played a pro-active role in the realm of sustainable development, taking part in several European initiatives and projects and setting up municipal networks. The latter, which connect cities scattered across Member States, may focus on specific environmental issues, such as sustainable mobility or energy, or include sustainable development in a wide range of policy priorities. These socio-ecological urban networks (hereafter SEUNs) have attracted growing academic attention. However, the bulk of the literature is located within Geography and Urban Studies, and it is more focused on the structure of the networks, the process of decision-making, and the policy outcomes than on the drivers of cities’ membership of SEUNs. Within this debate, the contribution of Political Science has been scant, and the political and economic drivers of cities’ engagement in European socio-ecological municipal networks have been overlooked. Understanding why local governments decide to participate in these networks is important for two main reasons: firstly, it contributes to shedding light on how contemporary local political elites govern cities within the European context; secondly, it allows us to understand why European cooperation for sustainable development has become a dominant discourse in urban politics. Conversely, this thesis adopts an urban approach to isolate the urban-level economic, political and institutional factors that impact on local authorities’ participations in European socio-ecological urban networks. Using a nested research design that combines a quantitative and qualitative analysis, the thesis seeks to shed light on the factors and motivations underlying the choice of cities to participate in European networks for sustainability. The results show that cities’ European commitment to sustainable development is part of a broad strategy to achieve urban regeneration. Therefore, participation in SEUNs is not necessarily motivated by environmental preoccupations but is functional to achieve economic and political objectives.

As much as urban areas are centres of greenhouse gas emissions, cities hold a unique position in tackling climate change as they have legal authority over key sectors such as buildings, transportation, and urban planning. Recognising the benefit of coordinating activities on the local level, transnational municipal networks (TMNs) unite local governments across borders, providing particular services to its members. In Europe, there are several TMNs focusing on issues related to climate protection. This study examines four of these networks (ICLEI, Climate Alliance, Energy Cities, EUROCITIES) and the functions they hold available. Interviews were conducted with representatives from the networks and a sample of German cities in order to depict both their perspectives. In terms of functions provided by the TMNs as a whole, lobbying for needs and concerns of the municipalities was considered as one of the networks’ main task. Further, two forms of lobbying were identified that varied depending on the respective network: lobbying, including mayoral support; and lobbying on a technical level. In addition, interviewees valued the exchange of information and experiences that these networks enable and foster. Lastly, their role in project management was stated as an important reason for network membership. A TMN-specific analysis revealed that ICLEI’s main strength was seen in lobbying on international level for its members’ concerns by also involving its member cities’ mayors. Municipalities seemed to turn to Energy Cities and EUROCITIES with regard to lobbying concentrated at EU decision-making, project cooperation, and the exchange of information. Climate Alliance’s unique selling point – since none of the other networks was associated with this function – appeared to be in organising awareness raising events and campaigns in cooperation with its members.