This book explores how the law of treaty withdrawal operates. Many commentators have observed a wider sense of crisis in international law as governments of different ideological stripes withdraw or threaten to withdraw from international organisations and treaties. There are different political forces behind all of these cases but, they all use the same basic device in international law - a treaty withdrawal clause. This book focuses on withdrawal clauses within multilateral treaties, providing a detailed synthesis of them and situating them within the wider context of the international rule of law. Yet, the theoretical assumptions about State behaviour upon which the law of withdrawal rests are fracturing. For it to operate, as the final part of this study shows, States have to behave as rational actors, averse to damaging their reputation in international law and willing to accept the existence of a wider rule-bound framework. Using insights from international relations and critical legal theory this book unpacks how and why the law of withdrawal operates and the forces that threaten its operation in the future.