Canon law differs from what commonly is thought of as "law" in that it is not enacted by a civil (or governmental) authority. Rather, canon law is ecclesiastical law, a code of provisions developed by a church. Specifically, canon law governs three religions in the world today, each having its own code of canon law--the Roman Catholic Church, the Eastern Orthodox Churches and the Anglican Communion of Churches. Other Protestant churches have laws, rules and policies, but do not consider these strictures to be canon law in the strictest sense of the word.
Canon law has its roots in the early Roman Catholic Church, initially being developed during the First Century A.D. at the Council of Jerusalem. The canon law of the Roman Catholic Church, having been used for nearly 2,000 years, is the oldest legal system to be found in the Western world. At the height of the Holy Roman Empire, canon law governed not only matters pertaining to the church but civil issues as well because the Catholic Church (in the person of the Pontiff) was both a religious and governmental authority.
The Codes of Canon Law of the three religions mentioned a moment ago govern the religious and to a significant degree the personal lives of the members to these churches. The Roman Catholic Church alone has more than 1 billion members worldwide. As a consequence, the individual Code of Canon Law of these churches theoretically has a significant impact on the lives of a large segment of the world's population.
Although the function of canon law has evolved over time, in today's world canon law governs the organization of the church itself. Canon law sets forth the manner in which members of the church are to conduct themselves not only in their relationship and interaction with the church but in their personal and civic lives (to some degree) as well.
The ultimate effects of canon law have been profound. Not only does canon law remain a vital code pertaining the lives of hundreds of millions of Christians all over the globe, all Western legal systems ultimately can trace their origins to early canon law. This includes both civil and common law legal systems as they have developed throughout all of Europe and North America.
There are two common misconceptions associated with canon law. First, many people wrongly assume that canon law largely is irrelevant today. What these individuals fail to understand that it is canon law is controlling the manner in which the largest group of Christians in the world worship and conduct their spiritual affairs. Second, other people believe that the heads of churches that adhere to canon law--specifically the Roman Catholic Pontiff--dictate all elements of canon law and are infallible when they make decisions in this regard. In fact, the last Pope to make a statement deemed to be infallible and an absolute matter of faith was Pius XII in 1950.