Ad Hoc Judge

An ad hoc judge (also called a judge ad hoc) is a temporary member of an international tribunal appointed by a state party to a particular case so that the party can be represented on the bench, even though none of the sitting permanent judges share its nationality. The institution is designed to preserve a sense of procedural equality between litigants and to give the court access to expertise on the legal system of the state concerned.

The most prominent example is at the International Court of Justice (ICJ), where the practice is codified in Article 31 of the Statute of the Court. If the ICJ already includes a judge of the nationality of one party, the other party may choose a judge ad hoc; if neither party has a national on the bench, both may choose one. The ad hoc judge participates in deliberations and votes on equal terms with elected judges, and must make the same solemn declaration of impartiality under Article 20.

Judges ad hoc are not required to be nationals of the appointing state, and in practice states sometimes nominate distinguished foreign jurists. For instance, in Nicaragua v. United States (1984–1986), Nicaragua chose a non-national to sit ad hoc.

The mechanism also exists, in varied forms, at the International Tribunal for the Law of the Sea (ITLOS) under Article 17 of its Statute, and at the European Court of Human Rights under Article 26 of the European Convention on Human Rights (as amended by Protocol No. 14), where an ad hoc judge sits when the elected national judge is unable to participate.

Critics argue the practice introduces an element of party-appointment that sits uneasily with full judicial independence; defenders counter that empirical studies show ad hoc judges do not always vote for their appointing party, and that the institution helps legitimize adverse rulings in the eyes of losing states.