Canon law
Main article: Canon law

The Corpus Juris Canonici, the fundamental collection of canon law for over 750 years.
Canon law (from Greek kanon, a 'straight measuring rod, ruler') is a set of ordinances and regulations made by ecclesiastical authority (Church leadership), for the government of a Christian organisation or church and its members. It is the internal ecclesiastical law governing the Catholic Church (both the Latin Church and the Eastern Catholic Churches), the Eastern Orthodox and Oriental Orthodox churches, and the individual national churches within the Anglican Communion.[102] The way that such church law is legislated, interpreted and at times adjudicated varies widely among these three bodies of churches. In all three traditions, a canon was originally[103] a rule adopted by a church council; these canons formed the foundation of canon law.

The Catholic Church has the oldest continuously functioning legal system in the western world,[104][105] predating the evolution of modern European civil law and common law systems. The 1983 Code of Canon Law governs the Latin Church sui juris. The Eastern Catholic Churches, which developed different disciplines and practices, are governed by the Code of Canons of the Eastern Churches.[106] The canon law of the Catholic Church influenced the common law during the medieval period[107] through its preservation of Roman law doctrine such as the presumption of innocence.[108]