In his youth Ignaz von Dӧllinger had been a leader of renewal of the Roman Catholic Church in Germany. He also had a strong interest in the institutional growth of Protestantism, and developed friendly relations with Protestants in Germany and outside. After 1850 his work seems more and more strongly marked by his realisation of the value of historical criticism. In Kirche und Kirchen. Papstthum und Kirchenstaat (1861) he argued that churches which separate themselves from the Pope end in chaos. At the same time, he himself was beginning to resist papal claims to absolute power. In 1871, unable to accept the teaching of Vatican I on Papal infallibility, he was excommunicated. Students were forbidden to attend his lectures. He was thus placed in circumstances which encouraged him, although they were personally very painful, to work actively for unity in the Church in such arenas as were open to him.

The protest against the Vatican I decrees in Germany contributed to the formation of the Old Catholic Churches. Döllinger was uncomfortable with anything which would set up ‘altar against altar’, and he found a constructive outlet for his concern in the Bonn Reunion Conferences of 1874 and 1875. These were held under Döllinger's presidency and included Old Catholics who had recently separated from Rome over the decrees of the Vatican Council, German Evangelicals, and a number of Anglicans.