A
- Abaddon
- Abbess
- Abbot
- Abdul Rahman Al Ghafiqi
- Abortion and Christianity
- Achaichus
- Action of Churches Together in Scotland
- Acts of the Apostles
- Additions to Daniel
- Adoration of the shepherds
- Advent
- Adventism
- Aeneas (biblical figure)
- Affinity (Christian organisation)
- African Methodist Episcopal Church
- African Methodist Episcopal Zion Church
- Agabus
- Agnus Dei
- Alexander (Ephesian)
- Alexander of Constantinople
- All Africa Conference of Churches
- Alliance of Baptists
- Alphaeus
- Alypius of Byzantium
- American-Canadian Macedonian Orthodox Diocese
- American Baptist Association
- American Baptist Churches USA
- Amish
- Anabaptism
- Ananias and Sapphira
- Ananias of Damascus
- Ananias son of Nedebaios
- Andrew the Apostle
- Andronicus of Pannonia
- Angel
- Anglican Church in North America
- Anglican Church of Australia
- Anglican Church of Canada
- Anglican Communion
- Anglicanism
- Anna the Prophetess
- Annas
- Anointing of Jesus
- Anselm of Canterbury
- Ante-Nicene Period
- Anti-Christian policies in the Roman Empire
- Antilegomena
- Antiochian Orthodox Archdiocese of Australia, New Zealand, and All Oceania
- Antiochian Orthodox Christian Archdiocese of North America
- Antipas of Pergamum
- Antonius Felix
- Antony I of Constantinople
- Antony II of Constantinople
- Apocalyptic literature
- Apollos
- Apostles
- Apostolic Age
- Apostolic Church of Pentecost
- Apostolic Fathers
- Archbishop
- Archbishop Atticus of Constantinople
- Archbishop Flavian of Constantinople
- Archbishop Maximianus of Constantinople
- Archbishop Maximus I of Constantinople
- Archbishop Nectarius of Constantinople
- Archbishop Sisinnius I of Constantinople
- Archdiocese of Thyateira and Great Britain
- Archippus
- Aretas IV Philopatris
- Arian controversy
- Arianism
- Aristarchus of Thessalonica
- Armenian Apostolic Church
- Arminianism
- Arrest of Jesus
- Arsacius of Tarsus
- Arsenios Autoreianos
- Ascension of Jesus
- Asia Pacific Baptist Federation
- Assemblies of God
- Assemblies of God in the United Kingdom
- Associated Presbyterian Churches
- Association of Baptist Churches in Ireland
- Association of Regular Baptist Churches
- Association of Vineyard Churches
- Assyrian Church of the East
- Athanasius of Alexandria
- Athenodorus of Byzantium
- Atonement in Christianity
- Augustine of Hippo
- Australian Christian Churches
- Australian Union Conference of Seventh-day Adventists
- Authorship of the Bible
- Avignon Papacy
- Azusa Street Revival