International law (also known as public international law and the law of nations) is the set of rules, norms, and standards generally recognized as binding between states. It establishes normative guidelines and a common conceptual framework for states across a broad range of domains, including war, diplomacy, economic relations, and human rights. Scholars distinguish between international legal institutions on the basis of their obligations (the extent to which states are bound to the rules), precision (the extent to which the rules are unambiguous), and delegation (the extent to which third parties have authority to interpret, apply and make rules).

The sources of international law includes international custom (general state practice accepted as law), treaties, and general principles of law recognised by most national legal systems. Although international law may also be reflected in international comity—the practices adopted by states to maintain good relations and mutual recognition—such traditions are not legally binding.

International law differs from state-based legal systems in that it is primarily—though not exclusively—applicable to states, rather than to individuals, and operates largely through consent, since there is no universally accepted authority to enforce it upon sovereign states. Consequently, states may choose to not abide by international law, and even to breach a treaty. However, such violations, particularly of customary international law and peremptory norms, can be met with disapproval by others and in some cases coercive action ranging from diplomatic and economic sanctions to war.

The relationship and interaction between a national legal system and international law is complex and variable. National law may become international law when treaties permit national jurisdiction to supranational tribunals such as the European Court of Human Rights or the International Criminal Court. Treaties such as the Geneva Conventions require national law to conform to treaty provisions. National laws or constitutions may also provide for the implementation or integration of international legal obligations into domestic law.