For over a millennium, Church law grew from the earliest ad hoc responses to particular problems of practice and discipline to an elaborate system called Canon Law. Early ecumenical councils promulgated their decisions in the form of “canons,” or laws. Meanwhile, many major decrees from powerful bishops and formal opinions from important theologians added to the increasing body of legislation. Influenced by the codes of civil law of the Emperor Justinian and others, medieval authorities began to systematize the massive and still expanding body of legal tradition. Gratian (d. c. 1179) first began to impose order on the chaos and remained an important authority in Roman Catholicism until his work was thoroughly revised in 1917.

Meanwhile, the Protestant Reformation brought about major changes in the new church bodies. Nearly all of the larger church organizations have developed legal structures of some kind to serve the concerns of what is called “church polity.” Often taking the form of articles, charters or conventions, the legal formulations of the various ecclesiastical bodies typically claim authority only within a particular family of churches. For example, the Southern Baptist, Northern Baptist, and National Baptist Conventions have all developed distinctive legislative and procedural frameworks within which to handle matters of policy and discipline. In this respect, Christians who follow Canon Law are similar to Jews who abide by rabbinical law and Muslims who follow Shari’a in their personal lives—the religious legal systems rarely if ever intrude into the civil law of the nation state in which the believers live.