The canon law of the Catholic Church (Latin for "canon law": ius canonicum[1]) is the system of laws and legal principles made and enforced by the hierarchical authorities of the Catholic Church to regulate its external organization and government and to order and direct the activities of Catholics toward the mission of the Church.[2] It was the first modern Western legal system[3] and is the oldest continuously functioning legal system in the West,[4][5] while the unique traditions of Eastern Catholic canon law govern the 23 Eastern Catholic particular churches sui iuris.

Positive ecclesiastical laws, based directly or indirectly upon immutable divine law or natural law, derive formal authority in the case of universal laws from promulgation by the supreme legislator—the supreme pontiff, who possesses the totality of legislative, executive, and judicial power in his person,[6] or by the College of Bishops acting in communion with the pope—while particular laws derive formal authority from promulgation by a legislator inferior to the supreme legislator, whether an ordinary or a delegated legislator. The actual subject material of the canons is not just doctrinal or moral in nature, but all-encompassing of the human condition. It has all the ordinary elements of a mature legal system:[7] laws, courts, lawyers, judges,[7] a fully articulated legal code for the Latin Church[8] as well as a code for the Eastern Catholic Churches,[8] principles of legal interpretation,[9] and coercive penalties.[10] It lacks civilly-binding force in most secular jurisdictions. Those who are versed and skilled in canon law, and professors of canon law, are called canonists[11][12] (or colloquially, canon lawyers[11][13]). Canon law as a sacred science is called canonistics.

The jurisprudence of canon law is the complex of legal principles and traditions within which canon law operates, while the philosophy, theology, and fundamental theory of Catholic canon law are the areas of philosophical, theological, and legal scholarship dedicated to providing a theoretical basis for canon law as legal system and as true law.