This article argues that Catholic universities should vigorously engage international law for at least three reasons. First, international law is an indispensible dialogue partner for Catholic Social Teaching (CST). Since CST belongs in Catholic higher education, so too does international law. Second, in numerous ways and on a global scale, international law raises the very questions of unity and diversity (disciplinary, perspectival, religious, and cultural) that Catholic universities, as "universities", can and must address. Third, given its secular character, international law challenges Catholic universities, as "Catholic", to engage, without sacrifice of faith-informed intellectual commitments, what Charles Taylor calls a "secular age."