Full communion is a kind of relationship between two or more organizations of Christians. It implies a unity between them unbroken by heresy or schism. Complete uniformity in theology and usage is not necessary for full communion: instead, different understandings and emphases are seen as mutually enriching. But agreement on orthodoxy of doctrine and willingness of the different organizations to be one body are essential.

When that unity is lacking, partial communion can still exist, because of the elements of Christian faith shared by the groups. For instance, the Roman Catholic Church sees itself as in partial communion with Protestant churches, and as in much closer, but still incomplete, communion with the Eastern Orthodox Churches (cf. Catechism of the Catholic Church, 838).[1]

The word “communion” is used not only of the bond uniting Christian individuals and groups, but also of groupings of Churches that explicitly recognize the existence between them of this bond in its full form. Examples are the Anglican Communion and the Porvoo Communion.

Full communion exists between:

• The constituent particular Churches of the Roman Catholic Church
• The (approximately 16) autocephalous Eastern Orthodox Churches
• The Coptic, Armenian Orthodox, Eritrean Orthodox, Jacobite, Indian Orthodox and Ethiopian Orthodox Tewahedo Churches (called "Oriental Orthodox" Churches)
• The Anglican Communion, the Old Catholic Church, and the Mar Thoma Syrian Church of India
• The Churches of the Porvoo Communion
• The Episcopal Church in the United States of America and the Evangelical Lutheran Church in America
• The Evangelical Lutheran Church in America, the Moravian Church, the Presbyterian Church USA, the Reformed Church in America, and the United Church of Christ.

In the case of the last-mentioned groupings, full communion means little more than an arrangement for:

• mutual recognition of members
• common celebration of the Lord's Supper/Holy Communion/Eucharist
• mutual recognition of ordained ministers
• mutual recognition of sacraments
• a common commitment to mission.

Full communion means much more for the first-mentioned. The constituent particular Churches of the Roman Catholic Church see each of them as the embodiment of the whole unique Catholic Church in a specific area. Similarly, each of the Eastern Orthodox Churches is viewed as a particular embodiment of the one Orthodox Church. This oneness is much weaker or almost entirely absent in the last-mentioned.

The first-mentioned also see sharing the Eucharist as the sign of full communion, the goal to which those striving for unity look forward. Others, especially those for whom the consecrated bread and wine are not really and truly, but only in a figurative sense, the body and blood of Christ, view this sacrament rather as a means of achieving unity by fostering togetherness.