In contrast to the accession procedure, the EU exit mechanism has not been put to the test. And yet, it has already been subject to considerable scholarly scrutiny. This stems not only from its recent (and controversial) inclusion in EU primary law (Art. 50 TEU), but also from the possible UK referendum on EU membership that could lead to its first ever use. A common critique in the literature is that the procedure of Article 50 TEU is formulated in an “incomplete”, “unclear”, if not “cryptic” fashion, thus generating “uncertainty”. The claim that is made in this Article is that in order to fully understand the application and the functioning of the withdrawal clause, it is necessary to accommodate the tension between the constitutional and international dimension of the EU legal order, tension inherent in the discipline of Article 50. In order to develop the argument, this Article first will discuss the withdrawal clause of the Lisbon Treaty itself. Second, this Article will add the issue of citizenship to the discourse on withdrawal, and it will evaluate whether this has any implications on how withdrawal by a Member State can be executed.