The International Court of Justice has jurisdiction over disputes between nations, and has decided dozens of cases since it began operations in 1946. Its academic defenders argue that the ICJ decides cases impartially and confers legitimacy on the international legal system. Its critics – mostly outside the academy – argue that the members of the ICJ vote the interests of the states that appoint them. Prior empirical scholarship is ambiguous. We test the charge of political bias using statistical methods. We find strong evidence that (1) judges favor the state that appoints them; (2) judges favor states whose wealth level is close to that of the judges’ own state; and (3) judges favor states whose political system is similar to that of the judges’ own state. We find weak evidence that judges are influenced by regional and military alignments.