Full communion is a mutual recognition between Christian churches or denominations that the partner churches hold "the essentials of the Christian faith". It includes

• 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 does not mean that the involved churches join into one denomination or forgo their distinctive traditions and theology.

Examples of churches in full communion:

• The twenty four catholic churches of the Papacy
• The sixteen autocephalous Eastern Orthodox Churches (for example, the Russian Orthodox Church and the Greek Orthodox Church)
• The Coptic, Armenian, Jacobite, and Tewahedo churches (infelicitously called "Oriental Orthodox" churches)
• The Anglican Communion, the Old Catholic Church, and the Mar Thoma Syrian Church of India
• The twelve churches of the Porvoo Communion
• The Episcopal Church, the Evangelical Lutheran Church in America, the Moravian Church, the Presbyterian Church USA, the Reformed Church in America, and the United Church of Christ.

Full communion is distinguished from partial communion such as exists between Catholics and Protestants, who recognize each other as their fellow Christians but are of different Christian denominations.

The word "communion" is also sometimes used as a synonym of "denomination", in the sense in which the latter word is used above.

Denominations that practice "closed communion" will only share the Eucharist (or Lord's Supper) with those with whom they are in full communion. Among those are the Roman Catholic and Eastern Orthodox churches. This is because their belief in Transubstantiation (ie that the bread and wine becomes the body and blood of Jesus Christ at the consecration during the Mass), they arguing that to allow those who do not believe in transubstantiation to take the Eucharist would be to show disrespect to Christ present in the bread and wine or even imperil the souls of those who partake improperly. Denominations that practice "open communion", most of whom do not share the belief in Transubstantiation and regard communion simply as a symbolic reenactment of the Last Supper, will typically also share the Lord's Supper with those with whom they are in partial communion.