The International Court of Justice (ICJ) has jurisdiction over disputes between nations and has decided dozens of cases since it began operations in 1946. Its defenders argue that the ICJ decides cases impartially. Its critics 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 bias using statistical methods. We find strong evidence that (1) judges favor the states that appoint them and that (2) judges favor states whose wealth level is close to that of the their own states, and weaker evidence that (3) judges favor states whose political system is similar to that of their own states and that (4) (more weakly) judges favor states whose culture (language and religion) is similar to that of their own states. We find weak or no evidence that judges are influenced by regional and military alignments.