Starting from a definition of constructivism and its uses in European integration, the chapter analyses the promises and limits of the approach for public policy studies at the EU level. The constructivist turn allowed for asking new questions with regard to European integration, such as, how do cognitive frames shape policies in the specific institutional context? Why do actors act as they do, beyond purely cost–benefit-based analysis, or in other words why do they define policy problems in a specific way? The answers to these questions helped to understand European integration not only as a federalist system, a functionalistic spillover project, or an intergovernmental entity whose progress is dependent on member state interests, but as a complex political system in which interests were embedded in cognitive frames. However, EU constructivist approaches slightly underestimated the power of actors to pick and choose adequate framings to defend their preferences. This limit was tackled in the most recent actor-centred perspective of constructivism which the chapter develops in more detail.