The Roman Catholic Church has the oldest continuously functioning legal system in the Western world, predating the common and European civil law traditions. What began with rules ("canons") adopted by the Apostles at the Council of Jerusalem in the 1st century has blossomed into a highly complex and original legal system encapsulating not just norms of the New Testament, but some elements of the Hebrew (Old Testament), Roman, Visigothic, Saxon, and Celtic legal traditions spanning thousands of years of human experience.
In the Catholic Church, positive ecclesiastical laws, based upon either immutable divine and natural law, or changeable circumstantial and merely positive law, derive formal authority and promulgation from The Pope, Who as Supreme Pontiff possesses the totality of legislative, executive, and judicial power in his person. The actual subject material of the canons is not just doctrinal or moral in nature, but indeed all-encompassing of the human condition.
In the early Church, the first canons were decreed by bishops united in "Ecumenical" councils (the Emperor summoning all of the known world's bishops to attend with at least the acknowledgement of the Bishop of Rome) or "local" councils (bishops of a region or territory). Over time, these canons were supplemented with decretals of the Bishops of Rome, which were responses to doubts or problems according to the maxim, "Roma locuta est, causa finita est" ("Rome has spoken, case is closed").
Later, they were gathered together into collections, both unofficial and official. The first truly systematic collection was assembled by the Camaldolese monk Gratian in the 11th century, commonly known as the Decretum Gratiani ("Gratian's Decree"). Pope Gregory IX is credited with promulgating the first official collection of canons called the Decretalia Gregorii Noni or Liber Extra (1234). This was followed by the Liber Sextus (1298) of Boniface VIII, the Clementines (1317) of Clement V, the Extravagantes Joannis XXII and the Extravagantes Communes, all of which followed the same structure as the Liber Extra. All these collections, with the Decretum Gratiani, are together referred to as the Corpus Juris Canonici.
By the 19th Century, this body of legislation included some 10,000 norms. Many these were difficult to reconcile with one another due to changes in circumstances and practice. This situation impelled Pope St. Pius X to order the creation of the first Code of Canon Law, a single volume of clearly stated laws. Under the aegis of the Cardinal Pietro Gasparri, the Commission for the Codification of Canon Law was completed under Benedict XV, who promulgated the Code, effective in 1918. The work having been begun by Pius X, it was sometimes called the "Pio-Benedictine Code" but more often the 1917 Code. In its preparation, centuries of material was examined, scrutinized for authenticity by leading experts, and harmonized as much as possible with opposing canons and even other Codes, from the Codex of Justinian to the Napoleonic Code.
Pope John XXIII initially called for a Synod of the Diocese of Rome, an Ecumenical Council, and an updating to the 1917 Code. After the Second Ecumenical Council of the Vatican (Vatican II) closed in 1965, it became apparent that the Code would need to be revised in light of the documents and theology of Vatican II. After multiple drafts and many years of discussion, Pope John Paul II promulgated the revised Code of Canon Law (CIC) in 1983. Containing 1572 canons, it is the law currently binding on the Latin (western) Catholic Church.
The canon law of the Eastern Catholic Churches, which had developed some different disciplines and practices, underwent its own process of codification, resulting in the Code of Canons of the Eastern Churches promulgated in 1990 by Pope John Paul II.
The institutions and practices of canon law paralleled the legal development of much of Europe, and consequently both modern Civil law and Common law bear the influences of canon law. Edson Luiz Sampel, a Brazilian expert in canon law, says that canon law is contained in the genesis of various institutes of civil law, such as the law in continental Europe and Latin American countries. Sampel explains that canon law has significant influence in contemporary society.
Currently, all catholic seminary students are expected to take courses in canon law (c. 252.3). Some ecclesiastical officials are required to have the doctorate (JCD) or at least the licentiate (JCL) in canon law in order to fulfill their functions: Judicial Vicars (c. 1419.1), Judges (c. 1421.3), Promoters of Justice (c. 1435), Defenders of the Bond (c. 1435) and Procurators - Advocates (c. 1483). In addition, Vicars General and Episcopal Vicars are to be doctors or at least licensed in canon law or theology (c. 478.1). Ordinarily, Bishops are to have advanced degrees in sacred scripture, theology, or canon law (c. 378.1.5).
St. Raymond of Penyafort (1175-1275), a Spanish Dominican priest, is the patron saint of canonists, due to his important contributions to the science of Canon Law.
The Greek-speaking Orthodox have collected canons and commentaries upon them in a work known as the Pedalion (Greek: Πηδάλιον, "The Rudder") so named because it is meant to "steer" the Church. The Orthodox Christian tradition in general treats its canons more as guidelines than as laws, the bishops adjusting them to cultural and other local circumstances. Some Orthodox canon scholars point out that, had the Ecumenical Councils (which deliberated in Greek) meant for the canons to be used as laws, they would have called them nomoi/νόμοι (laws) rather than kanones/κανόνες (standards), but almost all Orthodox conform to them. The dogmatic decisions of the Councils, though, are to be obeyed rather than to be treated as guidelines, since they are essential for the Church's unity.
In the Church of England, the ecclesiastical courts that formerly decided many matters such as disputes relating to marriage, divorce, wills, and defamation, still have jurisdiction of certain church-related matters (e.g., discipline of clergy, alteration of church property, and issues related to churchyards). Their separate status dates back to the 12th century when the Normans split them off from the mixed secular/religious county and local courts used by the Saxons. In contrast to the other courts of England the law used in ecclesiastical matters is at least partially a civil law system, not common law, although heavily governed by parliamentary statutes. Since the Reformation, ecclesiastical courts in England have been royal courts. The teaching of canon law at the Universities of Oxford and Cambridge was abrogated by Henry VIII; thereafter practitioners in the ecclesiastical courts were trained in civil law, receiving a Doctor of Civil Law (D.C.L.) degree from Oxford, or an LL.D. from Cambridge. Such lawyers (called "doctors" and "civilians") were centred at "Doctors Commons," a few streets south of St Paul's Cathedral in London, where they monopolized probate, matrimonial, and admiralty cases until their jurisdiction was removed to the common law courts in the mid-19th century. (Admiralty law was also based on civil law instead of common law, thus was handled by the civilians too.) Charles I repealed Canon Law in 1638 after uprisings of Covenanters confronting the Bishops of Aberdeen following the convention at Muchalls Castle and other revolts across Scotland earlier that year.
Other churches in the Anglican Communion around the world (e.g., the Episcopal Church in the United States, and the Anglican Church of Canada) still function under their own private systems of canon law.
In Presbyterian and Reformed Churches, canon law is known as "practice and procedure" or "church order," and includes the church's laws respecting its government, discipline, legal practice and worship.
The Book of Discipline contains the laws, rules, policies and guidelines for The United Methodist Church. Its last edition was published in 2004.