The diaconate is one of three ordained offices in the Roman Catholic, Anglican, Eastern Orthodox, and Oriental Orthodox churches. The other two offices are those of priest and of bishop. It is also an office in many Protestant denominations. The word deacon is derived from the Greek word diakonos (διακονος), which is often translated servant. The office of deacon originated in the selection of seven men (among them St Stephen) to assist with the pastoral and administrative needs of the early church. (Acts of the Apostles, chapter 6)

In Roman Catholic, Anglican and Orthodox churches, deacons assist priests in their pastoral and administrative duties, but (in Eastern Orthodoxy) report directly to the bishop. They have a distinctive role in the liturgy, their main tasks being to read the Gospel and assist in the administration of the Eucharist. In Orthodox churches, the deacon's main tasks also include censing the icons and people, calling the people to prayer and praying the "litanies" or series of petitions.

In Roman Catholic and Anglican churches, deacons often work directly in ministry to the marginalized inside and outside the church: the poor, the sick, the hungry, the imprisoned.

In the Anglican church, deacons are permitted to marry, as are priests. In the Catholic and Orthodox churches, a deacon may not marry after being ordained, but may be ordained if he is already married. See clerical celibacy.

In the modern Roman Catholic and Anglican churches, ordination to the diaconate has often been regarded as a transitional stage before ordination to the priesthood. However, in recent years greater recognition has been given to the distinctive role of 'permanent' deacons who do not become priests.

Deacons are also appointed or elected in many Protestant denominations, though this is less commonly seen as a step towards the Ministry. The role of deacon in Protestant denominations often varies a great deal from denomination to denomination; often, there will be more emphasis on administrative duties than on pastoral or liturgical duties. In some denominations, deacons duties are only financial management and practical aid and relief. Elders handle pastoral and other administrative duties.

For the role of Deacon in The Church of Jesus Christ of Latter-Day Saints (LDS/Mormon), see Priesthood (Mormonism).