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 persons 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, in order to ensure continuity within the court.
Should a judge die in office, the practice has generally been to elect a judge of the same nationality to complete the term. No two 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, this has meant common law, civil law and socialist law (now post-communist law). Since its creation, four of the five permanent members of the Security Council (France, Russia, the United Kingdom, and the United States) have always had a judge on the Court. The exception was China (the Republic of China until 1971, the People’s Republic of China from 1971 onwards), which did not have a judge on the Court from 1967–1985, because it did not put forward a candidate. The rule on a geopolitical composition of the bench exists despite the fact that there is no provision for it in the Statute of the ICJ.
Article 6 of the Statute provides that all judges should be “elected regardless of their nationality among persons of high moral character”, who are either qualified for the highest judicial office in their home states or known as lawyers with sufficient competence in international law. Judicial independence is dealt with specifically in Articles 16–18. Judges of the ICJ are not able to hold any other post, nor act as counsel. In practice the Members of the Court have their own interpretation of these rules. This allows them to be involved in outside arbitration and hold professional posts as long as there is no conflict of interest. A judge can be dismissed only by a unanimous vote of other members of the Court. Despite these provisions, the independence of ICJ judges has been questioned. For example, during the Nicaragua Case, the USA issued a communiqué suggesting that it could not present sensitive material to the Court because of the presence of judges from Eastern bloc states.
Judges may deliver joint judgments or give their own separate opinions. Decisions and Advisory Opinions are by majority and, in the event of an equal division, the President’s vote becomes decisive. Judges may also deliver separate dissenting opinions.
Ad hoc judges
Article 31 of the statute sets out a procedure whereby ad hoc judges sit on contentious cases before the Court. This system allows any party to a contentious case to nominate a judge of their choosing. It is possible that as many as seventeen judges may sit on one case.
This system may seem strange when compared with domestic court processes, but its purpose is to encourage states to submit cases to the Court. For example, if a state knows it will have a judicial officer who can participate in deliberation and offer other judges local knowledge and an understanding of the state’s perspective, that state may be more willing to submit to the Court’s jurisdiction. Although this system does not sit well with the judicial nature of the body, it is usually of little practical consequence. Ad hoc judges usually (but not always) vote in favor of the state that appointed them and thus cancel each other out. 
Generally, the Court sits as full bench, but in the last fifteen years it has on occasion sat as a chamber. Articles 26–29 of the statute allow the Court to form smaller chambers, usually 3 or 5 judges, to hear cases. Two types of chambers are contemplated by Article 26: firstly, chambers for special categories of cases, and second, the formation of ad hoc chambers to hear particular disputes. In 1993 a special chamber was established, under Article 26(1) of the ICJ statute, to deal specifically with environmental matters (although this chamber has never been used).
Ad hoc chambers are more frequently convened. For example, chambers were used to hear the Gulf of Maine Case (Canada/USA). In that case, the parties made clear they would withdraw the case unless the Court appointed judges to the chamber who were acceptable to the parties. Judgments of chambers may have less authority than full Court judgments, or may diminish the proper interpretation of universal international law informed by a variety of cultural and legal perspectives. On the other hand, the use of chambers might encourage greater recourse to the Court and thus enhance international dispute resolution.
As of 27 April 2012, the composition of the Court is as follows: