The terms Old Catholic Church, Old Catholics, Old-Catholic churches, or Old Catholic movement, designate "any of the groups of Western Christians who believe themselves to maintain in complete loyalty the doctrine and traditions of the undivided church but who separated from the See of Rome after the First Vatican Council of 1869–70".

The expression Old Catholic has been used from the 1850s by communions separated from the Roman Catholic Church over certain doctrines, primarily concerned with papal authority and infallibility. Some of these groups, especially in the Netherlands, had already existed long before the term. The Old Catholic Church is separate and distinct from Traditionalist Catholicism.

Two groups of Old Catholic churches currently exist: the Union of Utrecht (UU, not to be confused with Unitarian Universalism) and the Union of Scranton (US). Neither group is in full communion with the Holy See. Member churches of the Union of Utrecht are in full communion with the Anglican Communion as well as the Evangelical Lutheran Church of Sweden and the Philippine Independent Church and many UU churches are members of the World Council of Churches. Other churches which claim to be Old Catholic yet are not members of the Union of Utrecht or Union of Scranton are Independent Old Catholics.

Both groups trace their beginning to the 18th century when members of the See of Utrecht refused to obey papal authority and were excommunicated. Later Catholics who disagreed with the Roman Catholic dogma of papal infallibility, as defined by the First Vatican Council (1870), were thereafter without a bishop and joined with the See of Utrecht to form the Union of Utrecht of the Old Catholic Churches. Today, Utrechter Union churches are found chiefly in Germany, Switzerland, the Netherlands, Austria, Poland, and the Czech Republic.

In 2008, the Polish National Catholic Church created the Union of Scranton and separated from the Union of Utrecht. This was done in protest of the older Union's decision to ordain women and bless same-sex marriages. The Nordic Catholic Church later joined the Union of Scranton as well.

In the pre-Reformation era, there were already disputes that set the stage for an independent bishopric of Utrecht between the Catholic Church and the Holy Roman Empire, notably during between the 11th to 15th centuries.

The northern provinces that revolted against the Spanish Netherlands and signed the 1579 Union of Utrecht, persecuted the Roman Catholic Church, confiscated church property, expelled monks and nuns from convents and monasteries, and made it illegal to receive the Catholic sacraments. As a result, priests and communities went underground. Groups would meet for the sacraments in the attics of private homes at the risk of arrest. Priests identified themselves by wearing all black clothing with very simple collars.

All the episcopal sees of the area, including that of Utrecht, had fallen vacant by 1580, because the Spanish crown, which since 1559 had patronal rights over all bishoprics in the Netherlands, refused to make appointments for what it saw as heretical territories, and the nomination of an apostolic vicar was seen as a way of avoiding direct violation of the privilege granted to the crown. The appointment of an apostolic vicar, the first after many centuries, for what came to be called the Holland Mission was followed by similar appointments for other Protestant-ruled countries, such as England, which likewise became mission territories. The disarray of the Roman Catholic Church in the Netherlands between 1572 and about 1610 was followed by a period of expansion of Roman Catholicism under the apostolic vicars, leading to Protestant protests.