FOUNDATION: Unit III. Human Rights in International Law 3 of 7

Main Sources of International Law

Peace Palace Gardens
at The Hague

The World Court (the International Court of Justice or ICJ) sits in The Hague, Netherlands, and hears cases between states. The basic rules of the World Court contain the core facts about international law.

According to the rules of the World Court, international law has two main sources:

For more information,
click here: World Court

Click each tab to learn more about treaties and customary international law.
  Customary International Law (CIL)  

Treaties are the means states use to spell out the terms of their relations on a particular issue. A tr eaty is similar to a legal contract or agreement, such as a lease or rental agreement for an apartment. States consent to the obligations that treaties spell out. As a source of international law, treaties specify international rules of conduct.

Not all treaties constitute a general or universal rule of international law. For instance, the North American Free Trade Agreement (NAFTA) between the US, Canada, and Mexico is law that concerns only those three countries, even though NAFTA does affect other states.

Treaties can be multilateral or bilateral.

In the absence of a treaty, states sometimes follow a consistent practice over a period of time and come to accept this practice as a binding legal obligation. Over time, other states adopt the practice because of its usefulness, and it becomes a general practice with a legal obligation attached to it. States who fail to follow this custom risk punishment, sanctions, and retaliation. The practice then has become part of customary international law (CIL).

Typical American sailing
vessel, circa 1870
For example, during the nineteenth century, Britain required its seagoing vessels to display colored lights to avoid collisions. Britain’s requirement eventually became international law. The Scotia case involved a collision between the American sailing vessel Berkshire and the British steamer Scotia. In 1872, the US Supreme Court ruled that the Berkshire had failed to display colored lights in accordance with British rule, which by then had become the required practice of other states and was, therefore, the “law of nations”.
Typical British steamer,
circa 1870

In another case, the Paquette Habana case in 1900, the US Supreme Court recognized that customary international law protects fishing boats from capture by belligerents during warfare.

Most of the international laws governing the freedom of the high seas, privileges and immunities of states, jurisdiction over territory, and the rights of aliens emerged first as customs before they be came laws.

Much of customary international law has been codified into specific treaties. Some treaties are regarded as an expression of customary international law. Judges and other legal officials play important roles in sorting out their complexities.

The World Court is only able to deal with disputes that states submit to it. Do you think states should be required to submit to the World Court for all broken laws? How much authority should the World Court be granted?

International Court of Justice
ICRC: Treaties and customary international humanitarian law