Many international obligations are subject to exceptions. These can be expressed in several ways: an obligation may be vitiated by the presence of one of its constitutive negative requirements, an obligation may be set aside by the application of another more specific rule, or an actor might have a right to act in a certain way notwithstanding a contrary obligation. Exceptions are also of fundamental practical importance: for example, they affect the allocation of the burden of proof. This volume provides a systematic and analytic study of exceptions to legal obligations in international law and defences for breaches of these obligations. It features contributions written by legal philosophers, who introduce various theoretical approaches to the role of exceptions, and scholars of international law, who elaborate on generic issues applicable to exceptions in international law as well as examine specific issues arising from exceptions in their respective areas of expertise. Topics covered include the use of force, international criminal law, human rights, trade, investment, environment, and jurisdictional immunities.