The two primary sources of international law are:
- Treaties: Treaties, also known as conventions, covenants, or agreements, are written agreements between two or more states. Treaties are considered the most important source of international law. They can cover a wide range of issues, such as human rights, trade, the environment, and the conduct of warfare. Treaties are binding on the states that have ratified or acceded to them. When a state becomes a party to a treaty, it assumes legal obligations and responsibilities under international law. Treaties can be bilateral (between two states) or multilateral (involving multiple states).
- Customary International Law: Customary international law is derived from the general and consistent practice of states, which is accompanied by a belief that such practice is legally required (opinio juris). It is based on long-standing customs and traditions that have been accepted as legally binding by states. Customary international law can develop over time through the actions and behaviors of states, even in the absence of a formal written agreement. It applies universally unless it is shown that a particular state consistently objected to the customary rule.
These two sources of international law, treaties, and customary international law, work together to provide a framework for regulating the behavior of states and other international actors in the international community. Other sources of international law include general principles of law recognized by civilized nations and judicial decisions and teachings of highly qualified publicists, which can be used as subsidiary means for the determination of rules of law.