Desire for the visible unity of the Church increased in the 20th cent. as growing doctrinal agreement between the major Christian denominations was reinforced by liturgical reforms. In the second half of the cent., there was also an increased openness in the attitude of the RC Church towards members of other communions.
Reunion with the Orthodox Church has frequently been attempted by W. Churches. After the short-lived union effected by the Council of Florence (1439), there were other less important rapprochements. Some Orthodox Churches sent observers to the Second Vatican Council, and in 1965 the mutual anathemas of 1054 between the E. and W. Churches were lifted. There have been contacts between the Orthodox and the C of E since the 18th cent. (now impeded by the ordination of women), and Orthodox Churches are engaged in discussions with the Oriental Orthodox Churches, the Old Catholics and Reformed Churches.
Since the 17th cent. there have been aspirations for reunion between the C of E and the RC Church, notably at the time of the Oxford and post-Tractarian movements and of the Malines Conversations (1921–5). There have also been several efforts to unite the English dissenting bodies with the Established Church, beginning with the abortive attempt at the Restoration to ‘comprehend’ Presbyterians and Independents. The Lambeth Conference of 1888 laid down four conditions for such a union (the Lambeth Quadrilateral). The main difficulty which emerged in conversations between the C of E and the Free Churches concerned questions of ministry; these figured largely in the abortive Anglican-Methodist Conversations and the proposals of the Churches' Council for Covenanting, set up in 1978, but rejected by the C of E in 1982.
Schemes for reunion between the C of E and foreign Protestant bodies have been discussed intermittently since the 16th cent. In the 20th cent. there were agreements to establish mutual Eucharistic hospitality between the C of E and various Lutheran State Churches in Europe. The Porvoo Agreement, reached in 1992, envisaged a relationship between the Anglican Churches of Britain and Ireland and the Nordic and Balkan Lutheran Churches with a common membership and interchangeable ministry: it was ratified by all the Churches except those of Latvia and Denmark. In 2001 a similar scheme brought the Evangelical Lutheran Church in America and the Episcopal Church into a relationship described as ‘full communion’, with interchangeable ministries.
While numerous negotiations have proved abortive, there have been a series of Church unions since the early 19th cent. Past divisions have been healed by Presbyterians in Scotland in 1847, 1900, and 1929, and in the USA in 1958 and 1983, and between Methodist bodies both in Britain and the USA. Across denominational boundaries, the Lutheran and Reformed Churches of Prussia were brought together in 1817 in the United Evangelical Church of Prussia, later constituted the Evangelical Church of the Union. Though not a full union, the Leuenberg Concord of 1973 brought together Lutherans and Reformed Churches in Europe; over 100 Churches, including some in Latin America and some Methodists, now declare themselves in full communion through the Leuenberg Church Fellowship. In 1972 the Presbyterian Church of England and the greater part of the Congregational Church of England and Wales united to form the United Reformed Church, joined in 1981 by the majority of the Disciples of Christ. Unions formed on a interdenominational basis include united Churches in Canada (formed in 1925), South India (1947), the Philippines (1948), Zambia (1965), Zaire (1970), North India (1970), Pakistan (1970), Bangladesh (1971), and Australia (1977). In these unions Presbyterians and Congregationalists have most often been involved; Anglicans entered only the unions on the Indian subcontinent. In Africa and Asia local unions have played an important part in indigenizing the Church, as several missionary-founded Churches have been succeeded by a single locally funded and locally led Church. In 1970 two world confessional organizations joined to form the World Alliance of Reformed Churches, which encourages its member Churches to enter into unions. See also Anglican-Roman Catholic International Commission; Consultation on Church Union; Ecumenical Movement; and Uniat Churches.