Full communion

In Christian ecclesiology, full communion is a relationship between church organizations, groups, and individuals that mutually recognize their sharing the essential doctrines of Christianity and "are able to recognize in one another the one, holy, catholic and apostolic church in its fullness". Thus a profession of faith is required of people wishing to enter into full communion with the Catholic Church, even if they have been members of a separate church whose sacraments the Catholic Church considers to be valid. Being "in full communion with the Catholic Church" is incompatible with denying what it has definitively proposed as its teaching on faith and morals.

For the Orthodox Church, the Catholic Church, the Oriental Orthodox churches and the Church of the East, full communion exists only between Christians who form a single church. In a weaker understanding of the phrase, "full communion" is instead a matter of practical relationship between denominations that fully retain their distinct identities.

As a practical matter for most Catholics, this affects whether or not a member of one Church may partake of the Eucharist celebrated in another, and for priests, whether or not they may concelebrate the Eucharist with priests of another Church. In each case, if the two Churches are in full communion, then they may.

The Catholic Church makes a distinction between full and partial communion. Where full communion exists, there is but one church. Partial communion, on the other hand, exists where some elements of Christian faith are held in common, but complete unity on essentials is lacking. For instance, the Roman Catholic Church sees itself as in partial communion with Protestants and in much closer, but still incomplete, communion with the Orthodox churches. It has expressed this distinction in documents such as Unitatis redintegratio, the Second Vatican Council's decree on ecumenism, which states: "... quite large communities came to be separated from full communion with the Catholic Church ... men who believe in Christ and have been truly baptized are in communion with the Catholic Church even though this communion is imperfect".

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