Sometimes known as the "World Court", ICJ is the principal judicial organ of the United Nations (UN) founded in 1946. Its statute is a multilateral agreement annexed to the charter of the United Nations. Located in the Hague, it replaced the former Permanent Court of International Justice, which had operated within the Hague, Netherlands, since 1922, which itself was the culmination of earlier international movements to promote international arbitration as an alternative to armed conflict. The court serves as a principal vehicle for furthering the UN's mandate to facilitate the peaceful resolution of international disputes, acting as a permanent, neutral, third-party dispute settlement mechanism rendering binding judgments in "contentious" cases initiated by one state against another.

Disputes may be placed before the court by parties upon conditions prescribed by the U.N. Security Council. No state, however, may be subject to the jurisdiction of the court without the state's consent. Consent may be given by express agreement at the time the dispute is presented to the court, by prior agreement to accept the jurisdiction of the court in particular categories of cases, or by treaty provisions with respect to disputes arising from matters covered by the treaty. The court also has the power to render advisory opinions at the request of international institutions such as the UN General Assembly.

After World War II, the United States became party to the statute and accepted the compulsory jurisdiction of the court on terms specified by the Senate, including the famous Connally amendment, in which the United States declined to give its consent to "disputes with regard to matters which are essentially within the domestic jurisdiction of the United States of America, as determined by the United States of America." Over the subsequent decade and a half the United States unsuccessfully initiated a series of cases against the USSR, Hungary, Czechoslovakia, and Bulgaria concerning aerial incidents in Europe.

The court as a whole had relatively few cases on its docket during the 1960s, but the United States successfully appealed to the ICJ to vindicate its position as a matter of legal right during the Iranian hostage crisis. A case initiated by Nicaragua in 1984 challenging U.S. support of the Contra militias and the mining of Nicaraguan ports proved to be a watershed in U.S. dealings with the court. After vigorously and unsuccessfully contesting the court's jurisdiction in a preliminary phase, the United States declined to appear on the merits and subsequently withdrew its consent to the compulsory jurisdiction of the court in 1985. However, the United States continues to be party to cases relying on other jurisdictional grounds.

The fact that ICJ is used infrequently suggests that most states prefer to handle their disputes by political means or by recourse to tribunals where the outcome may be more predictable or better controlled by the parties. A 1993 case filed by Bosnia against the former Yugoslavia for violating the Genocide Convention was still pending in 2003, as was a matter between the Republic of Congo and France over alleged crimes against humanity. Trials against individuals for alleged war crimes against humanity or genocides involving Bosnia, Croatia, Kosovo, Serbia, and the former Yugoslavia were being handled by the International Criminal Tribunal for the former Yugoslavia, a separate U.N. tribunal. The ICJ has been maligned for the inconsistency of its decisions and its lack of real enforcement power. But its ambitious mission to resolve disputes between sovereign nations makes it a valuable source of support for many countries in their political interaction with other countries.