An ecumenical council (or oecumenical council; also general council) is a conference of ecclesiastical dignitaries and theological experts convened to discuss and settle matters of Church doctrine and practice. The word "ecumenical" derives from the Greek language "οἰκουμένη", which literally means "the inhabited world", – a reference to the Roman Empire that later was extended to apply to the world in general. Due to schisms, only the two earliest councils can be considered to have included bishops of the entire Christian Church, as it existed before those schisms. Later councils included bishops of only parts of the Church as previously constituted, leading the Christians who do not belong to those parts to reject the actions of those councils.

Acceptance of these councils thus varies between different branches of Christianity. Disputes over christological questions have led certain branches to reject some of the councils that others accept.

The Church of the East (accused by others of adhering to Nestorianism) accepts as ecumenical only the first two councils. Oriental Orthodox Churches accept the first three. Both the Eastern Orthodox Church and Roman Catholic Church recognise as ecumenical the first seven councils, held from the 4th to the 9th century; but while the Eastern Orthodox Church accepts no later council or synod as ecumenical, the Roman Catholic Church continues to hold general councils of the bishops in full communion with the Pope, reckoning them as ecumenical, and counting in all, including the seven recognized by the Eastern Orthodox Church, twenty-one to date. Anglicans and confessional Protestants, accept either the first seven or the first four as Ecumenical councils.

Paul VI (Latin: Paulus PP. VI; Italian: Paolo VI), born Giovanni Battista Enrico Antonio Maria Montini (26 September 1897 – 6 August 1978), reigned as Pope of the Catholic Church from 21 June 1963 until his death on 6 August 1978. Succeeding Pope John XXIII, who had convened the Second Vatican Council, he decided to continue it. He fostered improved ecumenical relations with Orthodox and Protestants, which resulted in many historic meetings and agreements.

Montini served in the Vatican's Secretariat of State from 1922 to 1954. While in the Secretariat of State, Montini and Domenico Tardini were considered as the closest and most influential co-workers of Pope Pius XII, who named him in 1954 Archbishop of Milan, the largest Italian diocese, yet denying him the Cardinal designation that traditionally accompanies being Archbishop of Milan, a function which made him automatically Secretary of the Italian Bishops Conference. John XXIII elevated him to the College of Cardinals in 1958, and after the death of John XXIII, Montini was considered one of his most likely successors.