In 1889, the bishops of the then-existing Old Catholic churches in the Netherlands, Germany, and Switzerland established their full ecclesiastical communion. This took the name of the Utrecht Union. Later, other bishops and their churches joined it. Today, the Utrecht Union of Old Catholic Churches comprises seven self-governing, episcopal-synodal churches in the following countries: the Netherlands, Germany, Switzerland, Austria, the Czech Republic, Croatia, and Poland (until 2003, this list included the Polish National Catholic Church in the USA and Canada). There are also Old Catholic communities in France, Italy, Sweden, and Denmark.
In 1890, the Old Catholic Congresses, which date back to 1871, were reconstituted and their international and ecumenical orientation was strengthened. The latter found resonance especially among members of the Anglican and Orthodox churches.
The Congress of Lucerne in 1892, at the request of the Old Catholic and Russian Orthodox representatives, decided to create an international scientific theological body. It pursued three key aims:
- To make the principles and teachings of the ancient Catholic Church known and resonant for the present moment;
- To promote the unification of the Christian churches by clarifying the issues that continue to divide them;
- To form an inter-church forum for these endeavours.
Early in 1893, the first issue appeared under the name Revue Internationale de Théologie. Editorship of the quarterly journal was in the hands of Prof. Dr. Eugène Michaud, who taught dogmatics and church history in French at the (Old) Catholic Theological Faculty at the University of Bern. Thanks to numerous collaborators from East and West, especially from the Orthodox and Anglican traditions, a significant compendium quickly emerged regarding questions of ecumenical understanding from the perspective of the Old Catholic church.
In 1911, as the authors and readership became predominantly German-speaking, the title of the outlet was changed to Internationale Kirchliche Zeitschrift – Neue Folge der Revue Internationale de Théologie (IKZ).
Subsequently, professors or former graduates from the Faculty of Old Catholic Theology in Bern have continued as the main editors.