Research on implementation in the European Union (EU) is characterized by a strong focus on legal conformance with EU policy. However, this focus has been criticized for insufficiently accounting for the implications of the EU's multilevel governance structure, thus providing an incomplete picture of EU implementation, its diversity and practice. The contributions of this collection represent a shift toward a more performance-oriented perspective on EU implementation as problem-solving. They approach implementation fundamentally as a process of interpretation of superordinate law by actors who are embedded within multiple contexts arising from the coexistence of dynamics of Europeanization, on the one hand, and what has been termed 'domestication', on the other. Moving beyond legal compliance, the contributions provide new evidence on the diversity of domestic responses to EU policy, the roles and motivations of actors implementing EU policy, and the 'black box' of EU law in action and its enforcement.