International law

International law derives its authority from several recognized sources rather than from one global code. Article 38 of the Statute of the International Court of Justice identifies international conventions, international custom, general principles of law, and judicial decisions and scholarly writings as subsidiary means for determining rules.¹ Treaties create written obligations for their parties, while customary international law develops from general state practice accepted as law. General principles can help resolve legal gaps, especially where procedural fairness or responsibility is at issue.

The United Nations Charter supplies a central constitutional framework, including rules on sovereign equality, peaceful settlement, and the prohibition on the threat or use of force.² The law is not confined to wartime diplomacy: it also governs the sea, trade, aviation, telecommunications, human rights, environmental protection, and diplomatic relations.

International law is enforced through a dispersed combination of courts, tribunals, national authorities, sanctions, and diplomatic consequences. The International Court of Justice hears contentious cases only when states have accepted its jurisdiction, and its judgments bind the parties in that particular case under the Court's Statute.¹ Other bodies handle narrower fields, including the International Criminal Court for certain crimes committed by individuals and specialized tribunals for the law of the sea, trade, or investment.

Compliance often occurs without formal litigation because governments value reciprocal observance, reputation, stable expectations, and access to cooperation. The UN Security Council can adopt binding measures under the Charter, although its permanent members' veto power can prevent collective action.² Domestic courts and agencies frequently give international rules practical effect by interpreting treaties, prosecuting crimes, or regulating conduct within national jurisdiction.

Treaties and customary international law interact, but neither automatically displaces the other. The Vienna Convention on the Law of Treaties codifies rules on treaty formation, interpretation, reservations, observance, amendment, and termination; its principle pacta sunt servanda requires treaties in force to be performed in good faith.³ A state generally becomes bound by a treaty through consent, while customary rules may bind states more broadly, subject to recognized qualifications.

Major fields include international humanitarian law, international human rights law, the law of the sea, international criminal law, refugee law, and international environmental law. The United Nations Convention on the Law of the Sea, for example, organizes maritime zones, navigation rights, resource jurisdiction, and dispute settlement.⁴ International criminal law differs from ordinary state responsibility by imposing liability on individuals for offenses such as genocide, crimes against humanity, and war crimes.⁵

Some of international law's most consequential rules arise at its edges. Peremptory norms, or jus cogens, are accepted and recognized by the international community as rules from which no derogation is permitted; a treaty conflicting with such a norm is void under the Vienna Convention.³ The International Law Commission has also distinguished custom's two elements: sufficiently general state practice and acceptance of that practice as law, known as opinio juris.⁶

Not every breach produces a lawsuit. State responsibility can require cessation, assurances of non-repetition, and reparation, while countermeasures are subject to limits and cannot justify violations of fundamental obligations. Individuals and organizations have gained standing or legal duties in specialized regimes, yet states remain the primary architects and holders of many rights. Maritime zones, diplomatic immunity, treaty reservations, and the law governing international organizations illustrate how technical rules often determine outcomes more quietly than headline disputes.

Customary international law

Rules arising from general state practice accepted as legally obligatory.

Jus cogens

A peremptory norm of general international law from which no derogation is permitted.

Pacta sunt servanda

The principle that treaties in force must be performed in good faith.

State responsibility

The legal consequences arising when a state commits an internationally wrongful act.

Opinio juris

The belief that a practice is followed because international law requires or permits it.