The Communion of Saints is a Christian doctrine held by the majority of major Christian churches. It is included in the Apostles Creed, the major confession of the Christian faith, laid down for the instruction of Christians between the 3rd and 6th century.

The doctrine of the Communion of Saints (based on 1 Corinthians 12:12-27 and Hebrews 12:1-2) is understood to mean that all saints (i.e., true Christians and faithful Old Testament Jews) are united in one body in Christ, and that this applies to Christians who are alive on earth, or living in Heaven (heavenly saints), whether Jewish or Gentile.

Roman Catholic, Eastern Orthodox, Oriental Orthodox and Coptic Churches, as well as some Anglicans, point to this doctrine as the basis for prayer to the (heavenly) saints. Such believers affirm that those saints who are in the presence of God in Heaven continue to help their fellow Christians on earth through prayer and intercession (Revelation 5:8), and that Christians on earth may request that intercession.

Furthermore, the Roman Catholic Church affirms that Communion of the Saints also includes the practice of prayers on behalf of the dead, meaning that Christians who have died but are not yet in the presence of God in heaven may benefit from the prayers of those on earth.

However, reasoning that only God can legitimately receive a prayer and that Purgatory is fiction, Protestants generally maintain that the Communion of Saints refers only to the unity of fellowship and the mutual responsibility of bearing one another's burdens and praying for one another in earthly life. The Eastern Orthodox Church also rejects the belief in Purgatory, although its members do offer prayers for the dead and affirm that communion of saints continues after death.