Established in 1945 by the UN Charter, the court began work in 1946 as the successor to the Permanent Court of International Justice. The Statute of the International Court of Justice, similar to that of its predecessor, is the main constitutional document constituting and regulating the court.
The court's workload covers a wide range of judicial activity. After the court ruled that the United States's covert war against Nicaragua was in violation of international law (Nicaragua v. United States), the United States withdrew from compulsory jurisdiction in 1986 to accept the court's jurisdiction only on a case-by-case basis. Chapter XIV of the United Nations Charter authorizes the UN Security Council to enforce Court rulings. However, such enforcement is subject to the veto power of the five permanent members of the Council, which the United States used in the Nicaragua case.
The ICJ is composed of fifteen judges elected to nine-year terms by the UN General Assembly and the UN Security Council from a list of people nominated by the national groups in the Permanent Court of Arbitration. The election process is set out in Articles 4–19 of the ICJ statute. Elections are staggered, with five judges elected every three years to ensure continuity within the court. Should a judge die in office, the practice has generally been to elect a judge in a special election to complete the term.
No two judges may be nationals of the same country. According to Article 9, the membership of the court is supposed to represent the "main forms of civilization and of the principal legal systems of the world". Essentially, that has meant common law, civil law and socialist law (now post-communist law).
There is an informal understanding that the seats will be distributed by geographic regions so that there are five seats for Western countries, three for African states (including one judge of francophone civil law, one of Anglophone common law and one Arab), two for Eastern European states, three for Asian states and two for Latin American and Caribbean states. For most of the court's history, the five permanent members of the United Nations Security Council (France, Russia, China, the United Kingdom, and the United States) have always had a judge serving, thereby occupying three of the Western seats, one of the Asian seats and one of the Eastern European seats. Exceptions have been China not having a judge on the court from 1967 to 1985, during which time it did not put forward a candidate, and British judge Sir Christopher Greenwood being withdrawn as a candidate for election for a second nine-year term on the bench in 2017, leaving no judges from the United Kingdom on the court. Greenwood had been supported by the UN Security Council but failed to get a majority in the UN General Assembly. Indian judge Dalveer Bhandari instead took the seat.