In the European Union (EU) policymakers “steer” via a rich body of secondary legislation, but leave the “rowing”, that is, the implementation and enforcement of EU law to the member states. Underlying this multilevel governance structure is the causal hypothesis that EU policies will induce the changes in the behavior of decentralized implementers needed to solving shared policy problems. However, several research-practical obstacles complicate empirically studying the practical implementation and outcomes of EU policies beyond legal compliance. Furthermore, EU rules change as they are being interpreted and adapted throughout the complex implementation chain. Both phenomena have recently been systematically conceptualized and operationalized as “practical implementation” and “customization”, respectively. This paper asks: How do legal compliance and the customization affect the practical application of EU rules? By combining these measures, the study provides systematic evidence on the effectiveness of EU law in 27 member states, based on conformity reports in the areas of environmental policy and justice and home affairs.
