International law is the body of legal rules and principles governing relations among states and regulating matters of international concern. It also establishes rights and obligations involving international organizations and individuals. Its subjects include territorial relations, armed conflict, human rights, environmental protection, and international commerce. Treaties, customary rules, and general principles provide its principal legal foundations; courts and international institutions interpret and apply them within their respective mandates. (un.org)
Scope and institutional structure
Public international law concerns international legal obligations, whereas private international law, also called conflict of laws, addresses cross-border private relationships: which court has jurisdiction, which law applies, and whether foreign judgments receive recognition or enforcement. International treaties can coordinate these national rules, so the two fields overlap without being identical. (hcch.net)
States remain central participants. The United Nations Charter recognizes their sovereign equality, while creating institutions with specified powers. International law therefore operates through both relations between states and organized cooperation within bodies such as the United Nations. Individuals are protected by human-rights obligations and may bear criminal responsibility under international criminal law. (un.org)
Sources of legal rules
Article 38 of the Statute of the International Court of Justice identifies the sources the Court applies: international conventions, international custom, and general principles of law. It also identifies judicial decisions and scholarly writings as subsidiary means for determining legal rules, rather than treating them as equivalent to treaties or custom. (icj-cij.org)
A treaty is an international agreement governed by international law. Its designation—such as convention, protocol, or charter—does not alone determine its legal character. The 1969 Vienna Convention on the Law of Treaties supplies rules concerning treaties between states, including their conclusion, interpretation, amendment, and termination. Treaties generally create obligations for their parties, not for third states without their consent. (treaties.un.org)
Customary international law requires two elements: a general practice and acceptance of that practice as law, commonly termed opinio juris. Repeated conduct alone is insufficient: it must be accompanied by a sense of legal obligation or entitlement, distinguishing legal custom from habit or courtesy. The International Law Commission’s 2018 conclusions provide guidance for identifying these elements. (legal.un.org)
General principles of law constitute another recognized source. Judicial reasoning helps determine the content of applicable rules, but Article 59 of the Court’s Statute limits the binding force of its decisions to the parties and the particular case. Consequently, the Court’s judgments do not automatically bind every state as precedents. (icj-cij.org)
Fundamental principles and treaty obligations
The Charter connects sovereignty with duties concerning peaceful dispute settlement and the prohibition of the threat or use of force. These principles structure international relations rather than leaving state conduct entirely unrestricted. The Charter also gives the Security Council powers to address threats to international peace and security, including sanctions and authorization of force under the relevant provisions. (un.org)
The treaty principle pacta sunt servanda requires agreements in force to be performed in good faith. Under the Vienna Convention, a party generally cannot invoke its internal law to justify non-performance. Treaty interpretation considers the ordinary meaning of terms in context and in light of the treaty’s object and purpose. (legal.un.org)
Some rules have a special status as peremptory norms, or jus cogens. The Vienna Convention defines these as norms accepted and recognized by the international community of states as a whole from which no derogation is permitted. A treaty conflicting with such a norm when concluded is void; an emerging peremptory norm renders a conflicting existing treaty void and terminates it. (legal.un.org)
Principal fields
International humanitarian law regulates armed conflict and protects persons not, or no longer, participating in hostilities. The Geneva Conventions of 1949 are central instruments. Human-rights law addresses states’ treatment of individuals, while international refugee law concerns the protection of refugees. These are distinct but complementary bodies of rules. (un.org)
Other fields govern navigation and maritime resources, international commerce, and environmental cooperation. The United Nations Convention on the Law of the Sea provides a treaty framework for maritime matters. International rules also address trade, disarmament, communications, outer space, and sustainable development. (un.org)
Dispute settlement and responsibility
International disputes may be addressed through negotiation, mediation, arbitration, or judicial settlement. The International Court of Justice resolves disputes between states only where the states concerned have accepted its jurisdiction. It also provides advisory opinions on legal questions referred by authorized UN organs and specialized agencies. (un.org)
State responsibility concerns the legal consequences of internationally wrongful conduct. The International Law Commission’s 2001 articles identify attribution to a state and breach of an international obligation as the basic elements. Consequences can include cessation, appropriate assurances of non-repetition, and full reparation through restitution, compensation, or satisfaction. The articles are not themselves a treaty. (legal.un.org)
The International Criminal Court differs from the International Court of Justice: it tries individuals, not interstate disputes. Its founding Rome Statute covers genocide, crimes against humanity, war crimes, and aggression, subject to jurisdictional and admissibility requirements. It complements national criminal systems and relies on state cooperation for arrests and enforcement. (icc-cpi.int)
Codification and development
The UN General Assembly has a Charter mandate to encourage progressive development and codification. The International Law Commission contributes draft texts and studies. Codification formulates and systematizes rules supported by existing practice; progressive development addresses fields not yet regulated, or insufficiently developed in state practice. These processes can produce draft articles, conclusions, or texts that subsequently become treaties, rather than automatically creating binding law upon publication. (legal.un.org)