There is a missing link between studies that investigate how regulation is becoming more similar, on the one hand, and studies that focus on how national policy styles and administrative traditions create patterns of stable diversity on the other. This article attempts to bridge these views in an analysis of how ideas transform as they transfer. The article shows that the idea of creating independent regulatory authorities (IRAs) has become institutionalized as a 'script' regarding how the regulation of liberalized electricity markets ought to be organized. This script has transferred to the European Union 15 Member States (EU-15) in processes moving from mimetic and normative to more coercive isomorphism, but the transformation is influenced by the way the need for credibility is mediated by contextual factors. Thus IRAs have more formal independence in countries formerly dominated by state ownership, where policy makers are perceived as corrupt and where decentralization is low. In this way, the analysis reveals how impulses of institutional change from the international arena are mediated by more stable and robust institutional factors at the domestic level. © 2006 (European Consortium for Political Research).