Representative democracy has been accorded constitutional status with the entry into force of the Lisbon Treaty. The European Parliament (EP) and the history of its empowerment embody this constitutional principle and its gradual institutionalization. To shed light on the EP's empowerment and the institutionalization of the principle of representative democracy in the EU, this article adopts a ‘domain of application’ approach. Instead of presenting rival theoretical approaches competing for explanatory superiority, the article shows that a more comprehensive picture of the EP's empowerment can be obtained by distinguishing between three types of institutional choice and associated explanations. Institutional creation, institutional change and institutional use are introduced as different types of institutional choice, and it is argued that each type gives primacy to particular explanatory mechanisms and dynamics to analyze the EP's empowerment.