Union of Utrecht (Old Catholic)

The Union of Utrecht of the Old Catholic Churches, most commonly referred to by the short form Union of Utrecht, is a federation of Old Catholic Churches, nationally organized from schisms which rejected Roman Catholic doctrines of the First Vatican Council in 1870; its member churches are not in communion with the Roman Catholic Church.

The 1889 Declaration of Utrecht is one of three founding documents together called the Convention of Utrecht. Many provinces of the Union of Utrecht of the Old Catholic Churches are members of the World Council of Churches. The UU is in full communion with the Evangelical Lutheran Church of Sweden; the Anglican Communion through the 1931 Bonn Agreement; the Philippine Independent Church, the Spanish Reformed Episcopal Church, and the Lusitanian Catholic Apostolic Evangelical Church through a 1965 extension of the Bonn Agreement; and, the Mar Thoma Syrian Church through the 2024 Thiruvalla agreement.

As of 2016, the UU includes six member churches: the Old Catholic Church of the Netherlands (OKKN), the Catholic Diocese of the Old Catholics in Germany, the Christian Catholic Church of Switzerland, the Old Catholic Church of Austria, the Old Catholic Church of the Czech Republic, and the Polish Catholic Church in Poland.