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Subject Guide

International Law

International Law is the body of rules that governs the legal relationships among sovereign states and other international actors, drawing primarily on treaties, customary international law, and general principles recognized by nations. It defines how states form binding obligations, exercise jurisdiction, bear responsibility for wrongful acts, and protect individuals through human rights and dispute-resolution mechanisms.

What International Law covers

International Law covers the sources, subjects, and enforcement of obligations that bind states across borders. It asks where international rules come from (treaties and custom), who is bound by them (states, and increasingly individuals and organizations), how states may regulate conduct that crosses borders (jurisdiction), and what happens when a state breaches an obligation (state responsibility and remedies). The subject also addresses the international protection of individuals through human rights and the forums available to resolve disputes, from negotiation and arbitration to the International Court of Justice. On law school and bar-style exams, International Law rewards precise rule statements and disciplined application: identify the source of the obligation, confirm it binds the relevant state, characterize the breach, and reason to the available remedy or defense. Because it sits at the intersection of public law and foreign relations, it overlaps with constitutional doctrine on treaty-making and the domestic effect of international rules.

Key topics

Treaties
A treaty is a written agreement between states governed by international law that, once consented to and in force, binds the parties under the principle pacta sunt servanda, subject to reservations, interpretation in good faith by ordinary meaning, and grounds for invalidity or termination.
Customary International Law
Customary international law arises from a general and consistent practice of states followed out of a sense of legal obligation (opinio juris), and it binds all states except a persistent objector, while peremptory norms (jus cogens) bind all states without exception.
Jurisdiction
A state's authority to prescribe, adjudicate, and enforce its law rests on recognized bases such as territoriality, nationality, the protective principle, passive personality, and universality, subject to limits including sovereign and diplomatic immunity.
State Responsibility
A state incurs responsibility when conduct attributable to it breaches an international obligation, giving rise to duties of cessation and reparation, unless a circumstance precluding wrongfulness (such as consent, force majeure, or lawful countermeasures) applies.
Human Rights
International human rights law imposes obligations on states to respect and protect the rights of individuals through customary norms and treaties, with certain core protections recognized as non-derogable even during emergencies.
International Dispute Resolution
States resolve disputes through peaceful means including negotiation, mediation, arbitration, and adjudication before bodies such as the International Court of Justice, whose contentious jurisdiction depends on state consent.

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Frequently asked questions

What are the primary sources of international law?
The primary sources of international law are treaties, customary international law, and general principles of law recognized by nations. Treaties are written agreements that bind their parties by consent, while custom arises from consistent state practice followed out of a sense of legal obligation. Judicial decisions and scholarly writings serve as subsidiary means for determining the content of these rules.
What is the difference between a treaty and customary international law?
A treaty is an express, written agreement that binds only the states that consent to it, whereas customary international law binds states based on general and consistent practice followed out of a sense of legal obligation (opinio juris). Custom generally binds all states except a persistent objector, while peremptory norms (jus cogens) bind every state without exception. A rule can exist in both treaty and customary form at the same time.
When is a state responsible for an internationally wrongful act?
A state is responsible when conduct that is attributable to it breaches an international obligation in force for that state. Attributable conduct includes acts of state organs and persons exercising governmental authority. Responsibility triggers duties to cease the wrongful conduct and make reparation, unless a circumstance precluding wrongfulness, such as consent, self-defense, force majeure, or a lawful countermeasure, applies.
How do states resolve international disputes?
States are obligated to settle disputes by peaceful means, including negotiation, mediation, conciliation, arbitration, and judicial settlement. The International Court of Justice hears contentious cases between states, but its jurisdiction depends on the consent of the states involved. Many treaties also designate specific tribunals or arbitration procedures for disputes arising under them.

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