The ideational impact captured by Manners's notion of normative power Europe (NPE) appears most distinct and potentially most consequential in the realm of regionalism. However, empirical research on the topic has been hampered by the focus on EU actorness and methodological difficulties. Drawing on diffusion theory, this article develops conceptual, theoretical and methodological foundations for conceiving NPE as ideational diffusion. It argues that Europe's ideational influence on regionalism can be fruitfully understood as the largely indirect process by which the EU experience travels to other regions through socialization and emulation. Yet, as structural conditions vary across regions, EU ideational diffusion rarely leads to similar or even comparable institutional practices and outcomes. A choice-orientated approach is proposed for examining these claims empirically, which focuses on specifying the underlying counterfactual: political decisions in regionalism would have been different in the absence of the EU. The article concludes by outlining the analytical and normative promise of the proposed recasting of Manners's original concept.