Canon Law, the ecclesiastical law of the Catholic Church, is a fully developed legal system, with all the necessary elements: courts, lawyers, judges, a fully articulated legal code and principles of legal interpretation. The academic degrees in canon law are the J.C.B. (Juris Canonici Baccalaureatus, Bachelor of Canon Law, normally taken as a graduate degree), JCL (Juris Canonici Licentiatus, Licentiate of Canon Law) and the J.C.D. (Juris Canonici Doctor, Doctor of Canon Law). Because of its specialized nature, advanced degrees in civil law or theology are normal prerequisites for the study of canon law.
In the first millennium of the Catholic Church, the canons of various ecumenical and local councils were supplemented with decretals of the popes; these were gathered together into collections such as the Liber Extra (1234), the Liber Sextus (1298) and the Clementines (1317).
Much of the jurisprudential style was adapted from the Roman Law Code of Justinian. As a result, Catholic ecclesiastical courts tend to follow the Roman Law style of continental Europe, featuring collegiate panels of judges and an investigative form of proceeding, called "inquisitorial", from the Latin "inquirere", to enquire. This is in contrast to the adversarial form of proceeding found in the Common Law system of English and U.S. law, which features such things as juries and single judges.
In the thirteenth century, the Catholic Church began to collect and organise its canon law, which after a millennium of development had become a complex and difficult system of interpretation and cross-referencing. In 1582 a compilation was made of the Decreta, Extra, the Sext, the Clementines and the Extravagantes (that is, the decretals of the popes from Pope John XXII to Pope Sixtus IV).
In response to the request of the bishops at the First Vatican Council, Pope Pius X ordered that work begin on reducing these diverse documents into a single code, presenting the normative portion in the form of systematic short canons shorn of the preliminary considerations ("Whereas ..." etc.) and omitting those parts that had been superseded by later developments.
The code was promulgated on 27 May 1917 as the Code of Canon Law (1917) (Latin: Codex Iuris Canonici) by his successor, Pope Benedict XV, who set 19 May 1918 as the date on which it came into force, . For the most part, it applied only to the Latin Church except when "it treats of things that, by their nature, apply to the Oriental", such as the effects of baptism (canon 87).
In the succeeding decades, some parts of the 1917 Code were retouched, especially under Pope Pius XII. In 1959, Pope John XXIII announced, together with his intention to call the Second Vatican Council, that the Code would be completely revised. In 1963, the commission appointed to undertake the task, decided to delay the project until the Council had been concluded. When work finally began, almost two decades of study and discussion on drafts of the various sections were needed before Pope John Paul II could promulgate the revised edition, which came into force on 27 November 1983, having been promulgated via the apostolic constitution Sacrae Disciplinae Leges of 25 January 1983.
This edition is referred to as the 1983 Code of Canon Law to distinguish it from the 1917 Code. Like the preceding edition, it applies to Catholics of the Latin Rite. For Eastern Catholics two sections of Eastern canon law had already, under Pope Pius XII, been put in the form of short canons. These parts were revised as part of the application of Pope John XXIII's decision to carry out a general revision of the Church's canon law; as a result a distinct Code for members of the Eastern Catholic Churches came into effect for the first time on 1 October 1991 (Apostolic Constitution Sacri Canones of 18 October 1990). The Code of Canons of the Eastern Churches, as it is called, differs from the Latin Code of Canon Law in matters where Eastern and Latin traditions diverge, such as terminology, discipline concerning hierarchical offices and administration of the sacraments.
In 1998, Pope John Paul II issued the motu proprio Ad Tuendam Fidem, which amended two canons (750 and 1371) of the 1983 Code of Canon Law and two canons (598 and 1436) of the 1990 Code of Canons of the Eastern Churches, so as to add "new norms which expressly impose the obligation of upholding truths proposed in a definitive way by the Magisterium of the Church, and which also establish related canonical sanctions."
Under the 1983 Code of Canon Law, all seminary students are required 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. 1419.4); judges (c. 1421.3); promoters of justice (c. 1435); defenders of the bond (c. 1435); procurators and 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 an advanced degree in 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. Other saintly patrons include St. Ivo of Chartres and St. Robert Bellarmine.