|Transnational City Networks (TCNs), intended as voluntary organisations formed by local authorities in order to pursue some kind of perceived collective interest/purpose (such as Eurocities or others issue-specific networks), are becoming crucial actors in the migration policy field. They have been enthusiatically depicted as ‘new coalitions’ in the European Multilevel Governance (MLG) of migration, which challenge state-centred modes of governing migration-related issues, while emphasising forms of horizontal coordination among cities and of vertical negotiation with EU institutions. Yet, studies that empirically assess such hypotheses are still few, while research carried out in other policy fields such as urban development and climate-change mitigation, demonstrate how national authorities continue to remain key gatekeepers for access to the resources needed to undertake local policies. In this chapter I present first of all evidence of the relevance of TCNs in the migration policy field by showing how they have been mobilising on the current refugee crisis. Therefore, I provide a state of the art of existing research on TCNs on migration policy to identify gaps and promises of this emerging research stream. Hence, as a third step, a framework to better conceptualise TCNs as key actors in the MLG of migration policy is presented. In particular, I look at TCNs as the product of simultaneous processes of activation from above, i.e. from EU or other supranational institutions; and of mobilisation from below, i.e. from the cities themselves, to establish horizontal, city-to-city forms of collaboration, by-pass national governments and link directly to supranational institutions. In this perspective, TCNs perform three main functions, i.e.: lobbying for favourable policies and for funding from supranational institutions; allowing for the establishment of cross-country/cross-city dialogues; promoting policy learning and the exchange of best practices. Along with these instrumental functions, which are usually acknowledged by TCNs websites and official documents, I argue for a theoretical framework aimed at shedding light onto cities’ perspective, therefore unravelling the reasons behind their decision to get involved in these networks. Especially when such a politically sensitive issue as migration is considered, participation in TCNs is likely to be praised first and foremost for the symbolic and political resources it may convey, such as strenghtening the city’s international identity in and positioning vis-à-vis other cities, legittimizing existing policies and/or local political élites. The chapter discusses both instrumental and symbolic functions, showing how the MLG approach can help to disentangle the complexity of TCN–city relations, the complexity of TCN–city relations, which do not necessiairly and always imply the ‘hallowing out’ of the nation-state, but rather its reinvention in the context of non-hierarchical and diffused MLG relationships.