Canon law in Western culture is the law of the Roman Catholic and Anglican churches. The Eastern Orthodox concept of canon law is similar to but not identical to the more legislative and juridicial model of the West. In both traditions, a canon is a rule adopted by a council (From Greek kanon/κανον, for rule, standard, or measure); these canons formed the foundation of canon law. In the Anglican church, the official Church of England, the Ecclesiastical Courts that formerly decided many matters such as disputes relating to marriage still have jurisdiction of certain church related matters; their jurisdiction dates back to the middle ages. In contrast to the other courts of England the law used in ecclesiastical matters is a civil law system, not common law.

In the Roman Catholic church, the canons of the councils were supplemented with decrees of the Popes, which were gathered together into collections called decretals.

In the 20th century, the Roman Catholic Church began attempting to codify canon law, which two millennia of development had become a complex and difficult system of interpretation and cross referencing. The first code of canon law was published in 1917. A revised code was published in 1983. Canon law within the Catholic Church is a fully developed legal system, with all the familiar trappings of courts (including lawyers); the highest degree of education in canon law is the J.C.D. (Juris Canonis Doctor, Doctor of Canon Law).

The Orthodox Christian tradition is generally much less legalistic, and treats many of the canons more as guidelines than as absolute laws, adjusting them to cultural and other local circumstances. Some Orthodox canon scholars point out that, had the Ecumenical Councils (which did their business in Greek) meant for the canons to be used as laws, they would have called them nomoi/νομοι (laws) rather than kanones/κανονες (standards).

Greek-speaking Orthodox have collected canons and commentery upon them in a work known as the Pedalion/Πεδαλιον (rudder--so called because it is meant to "steer" the Church). However, this is not a codification, but simply a compilation of one tradition of interpretation of the canons.