John VIII may refer to:

• Pope John VIII, Pope from 872 to 882
• Antipope John VIII, antipope in 844
• John VIII bar Abdoun, Syriac Orthodox Patriarch of Antioch (944-1033)
• John VIII of Constantinople, Patriarch of Constantinople (1010-1075)
• John VIII Palaiologos, Byzantine Emperor (1392–1448)
• John VIII, Count of Harcourt, 1398–1424
• John VIII, Count of Vendôme, 1426–1477
• John VIII, Archbishop of Antivari, d. 1571
• John VIII, Count of Nassau-Siegen, 1583–1638
• The mythical Pope Joan, in some versions of her legend

See also

• John 8, the eighth chapter of the Gospel of John