This paper considers whether the United Kingdom’s notification under Article 50 TEU on 29 March 2017 can be unilaterally revoked. The article also considers the right of states to revoke of unilateral notifications of withdrawal from multilateral treaties more generally due to the fact that the United Kingdom’s right to withdraw its Article 50 TEU notification is (at least in part) dependent on an applicable right of withdrawal in customary international law. The paper addresses the applicability of Article 68 the Vienna Convention of the Law of Treaties (VCLT) to the Article 50 TEU unilateral revocation debate paying particular attention to the drafting history of the article as well as the arguments for and against the customary status of any right of unilateral revocation of instruments of withdrawal from multilateral treaties. The article also examines whether Article 50 TEU, by express words or necessary implication, excludes the operation of any alleged customary right to unilaterally revoke an instrument of withdrawal before it takes effect.