Unitatis Redintegratio

Unitatis redintegratio (Latin for "Restoration of unity") is the Second Vatican Council's decree on ecumenism. It was passed by a vote of 2,137 to 11 of the bishops assembled, and was promulgated by Pope Paul VI on 21 November 1964.

The numbers given correspond to the section numbers within the text.

Unitatis Redintegratio calls for the reunion of Christendom and so it is not terribly different from previous calls for unity by Pope Leo XIII in the 1894 encyclical Praeclara gratulationis publicae. However, the document articulates a different kind of ecclesiology than Praeclara, focusing on the unity of the people of God and on separate Christian brethren instead of a classical call for schismatics to return to the fold under the unity of the Vicar of Christ.

The document acknowledges that there are serious problems facing prospects of reunion with Reformation communities that make no attempt to claim apostolic succession such as the Anglican communion does. Ecclesial communities that adhere to Calvinism are a particular case because they often have important doctrinal differences on key issues such as ecclesiology, liturgy and mariology. Other communities have insoluble doctrinal differences with Catholic Christianity because their theology of the Holy Trinity is manifestly incompatible with the doctrine of the council of Nicea in the early Church. That these serious problems are a barrier to salvation is clarified in the 2004 Vatican document, "The Decree on Ecumenism, Read Anew after Forty Years".

The concept and wording was published as late as 1793, in a discourse which examined two papal briefs to the Bishop of Chiusi-Pienza. Frank Flinn wrote, in Encyclopedia of Catholicism, that in 1959 Pope John XXIII "addressed Protestants as separated brethren," in Ad Petri cathedram (APC), which Flinn saw as "an important step toward recognizing Protestants as legitimate partners in a future dialogue." But Pope Leo XIII "was the first to speak of 'separated brothers'" according to John Norman Davidson Kelly's A Dictionary of Popes. Edward Farrugia, in Gregorianum, describes the development from Pope Leo XIII's Orientalium dignitas (OD) to Orientalium Ecclesiarum (OE) to Unitatis Redintegratio (UR). "Yet if OE builds on OD, differences remain. Whereas OD" 186 "speaks of 'dissident bretheren' (fratres dissidentes), OE 28 speaks of 'separated bretheren' (fratres seiunctos), although it does not go as far as UR 14, where there is an inchoative use of the language of 'sister Churches' (inter Ecclesia locales, ut inter sorores)." Farrugia noted Austin Flannery's translations in Vatican Council II, "OE 29 speaks of the 'separated Churches' and OE 25 of 'any separated Eastern Christians', and OE 29 of 'Eastern separated brethren'." J. M. R. Tillard goes into detail, in New Catholic Encyclopedia, about "the development of a carefully nuanced vocabulary, consistent with Vatican II Ecclesiology," which evolved from "the idea of membership in favor of that of incorporation" and has its categorization found in the dogmatic constitution Lumen gentium (LG) which Tillard describes:

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