Ioannes III

Ioannes III (, Iōannēs G΄) may refer to:

• Patriarch John III of Constantinople (died in 577)
• John III Doukas Vatatzes (c. 1192–1254), Byzantine Emperor
• John III Megas Komnenos (c. 1321–1362), Emperor of Trebizond

See also

• John III (disambiguation)