Together with its further widening and deepening, the character of the EU has changed fundamentally during the last two decades. Acknowledging this development, the politics-dimension has become visibly more relevant in research on the EU. This “politics turn” is accompanied by an increased interest in research on political behavior of individual and collective actors—voters, parties, interest groups, executive agencies, mass and social media—in the EU multi-level system. The objectives of this thematic issue are to conceptually, empirically, and methodologically capture the different facets of this newly emerged interest in actors’ political behavior in the EU multi-level system. To this end, the thematic issue strives to highlight the connections between political processes and behavior at the European level and other political layers in the EU Member States’ multi-level systems. In particular, we aim to broaden the scope of research on political behavior in the EU and its strong focus on electoral politics across multiple levels of government. To this end, the thematic issue links research on voting behavior with work on party competition, electoral campaigns, public opinion, protest politics, responsiveness, (interest group) representation, government and opposition dynamics, and parliamentary behavior more broadly to the multi-layered systems within EU Member States.