Despite their common goals and historical connections, European and U.S. fundamental rights jurisprudence are often two ships passing in the night. This Working Paper addresses a key element of that jurisprudence—freedom of religion—and asks what the two bodies of law could learn from one another. It first outlines the contours of religious freedom law under the U.S. Supreme Court, the European Court of Human Rights, and the Court of Justice of the European Union. It then contrasts the U.S. and European approaches and identifies key conceptual differences. These material differences include (i) whether a religious adherent is “exercising” or “manifesting” religion at all; (ii) whether, and to what extent, courts may balance the rights of religious adherents against the rights of others in society; and (iii) whether, and to what extent, claims sounding in religious liberty should be assessed in light of other fundamental rights. This Working Paper concludes that understanding these differences could enrich and improve U.S. constitutional law on freedom of religion.