AbstractSet in the context of the larger literature on regionalist parties and specifically on the Italian Northern League, this paper examines and explains why the party moved from Euro-positivism to Euroscepticism. Drawing on concepts raised in the larger comparative politics literature, five explanations of this U-turn towards Europe are evaluated. It is argued that, despite the strength of explanations that focus on the desires of party supporters, the role of public opinion, the potential influence of economic investors or the role of EU-level institutions in shaping party preferences, a more cogent explanation focuses on domestic-level developments. The conclusions will underscore the general implications of this research for the study of parties, particularly regionalist ones in the EU, highlighting that a party's changing stance towards supranational integrationist polices can be best understood as a consequence of its experience in a political system's electoral system.