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 overview of their operation, drawing on a range of case studies including Brexit, nuclear weapons treaties and investment arbitration agreements. The obligations a withdrawal clause places on a withdrawing state help regulate the withdrawal process, providing a notional form of stability. Using insights from international relations theory and legal theory, this book unpacks how and why the law of withdrawal operates and what its limitations are.