A canon (from the Latin canonicus, itself derived from the Greek κανονικός, kanonikós, "relating to a rule", "regular") is a member of certain bodies subject to an ecclesiastical rule.

Originally, a canon was a cleric living with others in a clergy house or, later, in one of the houses within the precinct of or close to a cathedral and conducting his life according to the orders or rules of the church. This way of life grew common (and is first documented) in the eighth century. In the eleventh century, some churches required clergy thus living together to adopt the rule first proposed by Saint Augustine that they renounce private wealth. Those who embraced this change were known as Augustinians or Canons Regular, whilst those who did not were known as secular canons.