International law is one of the basic building blocks of the United Nations system. It provides the foundation for stable, peaceful and just relationships between States and their people. This week, we’ll explore what international law is.

What is International Law and What isn’t

The United Nations defines international law as “the legal responsibilities of States in their conduct with each other, and their treatment of individuals within State boundaries.” International law is established in four primary ways: treaties, judicial decisions, some Security Council actions and custom.

The most familiar of these ways is treaties. Most international law is established by States agreeing that a certain principle, norm or procedure is indeed international law. Treaties are formal, legally-binding documents that establish these agreements by States. They are drafted and signed by States, which have a legal obligation to obey the terms of a treaty they have signed. While the majority of treaties in the world are bilateral (between two States), the most commonly referenced treaties in Model UN are multilateral treaties that include many States.

International courts can also establish international law. Courts are given the power to create binding decisions by treaties signed by States. All opinions by the International Court of Justice (ICJ) in contentious cases brought by two States before the court are legally-binding and constitute international law but do not create precedents for future cases. Advisory opinions, on the other hand, are not binding. The ICJ derives its authority from a particularly important treaty: the United Nations Charter. Other treaties have established other courts that make legally-binding decisions as well, such as the International Criminal Court, and the International Tribunal for the Law of the Sea.

Some Security Council actions establish legally-binding obligations under international law. Any action taken by the Security Council under Article VII related to securing international peace (such as through peacekeeping or sanctions) is legally-binding on all Member States. Additionally, the Security Council can establish ad hoc tribunals that can make legal decisions. Two former examples are the International Criminal Tribunal for Rwanda (ICTR) and the International Criminal Tribunal for Yugoslavia (ICTY).

Finally, customary international law can be binding upon States. The Statute of the International Court of Justice defines customary international law as “evidence of a general practice accepted as law.” Customary international law is defined by the general practice of States and by acceptance as law by States. In practice, customary international law is complicated. States can (and do) regularly redefine customary international law simply by changing their practices.

There are many other UN documents that appear to be legally binding but are not. Declarations, Agreements, and Ministerial Statements are not legally binding documents. They do not carry the weight of international law.

Treaty Terminology

Treaty is one of the most common terms for a multilateral agreement, though many are called conventions or covenants. Treaties, conventions and covenants are synonymous, with no distinction in meaning. Protocols are also legally-binding agreements, though they are typically an addendum to another treaty. For example, the Kyoto Protocol is an addendum to the UN Framework Convention on Climate Change, while Protocol I is an addition to the four Geneva Conventions.

States are bound only by treaties they have agreed to. States bound by a treaty are referred to as the States Parties (pronounced States Party)—the parties to the agreement. States become States Parties in two primary ways: by ratifying a treaty and acceding to a treaty.

Ratification occurs when a State formally agrees to be bound by a treaty. Accession typically occurs when a new State takes on the legal obligations of a former State, such as when Russia acceded to the treaty obligations of the USSR. Ratification is more typical. Signatures are different from ratification or accession. Signatures occur soon after a new treaty is created and they signal a State’s intent to ratify a treaty. A signature alone is not legally binding.