This research develops a novel analytical framework to analyze urban Europeanization processes based on the concept of the city as a collective actor. Specifically, it distinguishes vertical (city-to-EU and national government) from horizontal (city-to-city) and internal (city-to-private sector, civil society, academia) interactions in European cities in the policy context of the largest European urban climate policy, the EU Cities Mission. Operationalizing a comparative qualitative case study approach involving semi-structured interviews and field visits, the research shows that the EU Cities Mission deepens urban Europeanization processes in the two Eastern European cities Kraków (Poland) and Liepāja (Latvia), thereby strengthening the local governance of the urban ecological transition through improved public sector coordination, stakeholder engagement and citizen involvement. This allows the European Commission to further its urban agenda from below, bypassing the nation state in a policy sector in which it has no formal competences. However, important structural barriers such as the administrative and financial capacity of cities, ownership over the net zero transition among municipal actors and citizens, and prior experience with EU projects, limit the mission’s transformative impact.
