Sovereignist claims are on the rise – in Europe, the USA, and beyond. In dealing with processes such as globalization and supranational integration, which have progressively shifted powers and competencies away from nation states, these transformations have created a fertile terrain for reactions against the sources of such insecurity, which find full expression in the sovereignist claims to ‘take back control’, that is to say to return to the traditional understanding of sovereignty being based upon mutually exclusive territories. These sources of insecurity and social unrest have also provided structures of political opportunity for the electoral success of populist parties. Despite its relevance for the understanding of the populist discourse, however, sovereignty has been largely under-theorised by scholars dealing with populism. Accordingly, we propose a new research agenda to study populist mobilization that focuses on the linkage between populism and sovereignism, while also encouraging further theoretical and empirical studies, focusing on both the demand side and the supply side. In particular, we suggest some crucial aspects with which the Special Issue seeks to engage, before pointing to some substantial implications that are likely to emerge from the findings of this research agenda.