This paper opens up the black box of enlargement, focusing on how the intra-organizational relationships among the Council of the European Union, the European Commission, and the European Parliament affect the process of enlargement. Formally speaking, enlargement is an intergovernmental process, suggesting that member states are firmly in control of its outcomes. However, the EU’s supranational actors, specifically the European Parliament and European Commission also attempt to influence enlargement at various stages. I posit that the process of enlargement to the Western Balkans has evolved, influenced by changing constraints which are operating on the aforementioned actors. The added value of this work is in disaggregating the enlargemen...