John III may refer to:
People Pope John II (III) of Alexandria, Patriarch of Alexandria from 505 to 516 John III (bishop of Jerusalem) in 516–524 Pope John III, Pope from 561 to his death in 574 John Scholasticus, Patriarch of Constantinople from 565 to his death in 577 Pope John III of Alexandria, Coptic Pope from 680 to 689 John III Rizocopo, Exarch of Ravenna from 710 to 711 John III the Philosopher, Catholicos of Armenia from 717 to 728 John III of the Sedre, Syriac Orthodox Patriarch of Antioch from 631 to his death in 648 John III of Naples, Duke from 928 to his death in 968 John III of Gaeta, Duke from 984 to his death in 1008 John III of Amalfi, Duke in 1073 John III Doukas Vatatzes (c. 1192 – 1254), Emperor of Nicaea John III Comyn of Badenoch (died 1306) John III, Duke of Brittany (1286–1341) John III, Duke of Brabant (1300–1355) John III Megas Komnenos (c. 1321 – 1362), Emperor of Trebizond John III of Montferrat (c. 1362 – 1381) John III, Burgrave of Nuremberg (c. 1369 – 1420) John III, Count of Auvergne (1467–1501) Ivan III of Russia (1440–1505), Grand Duke of Russia since 1462 John III of Navarre (1469–1516) John III Crispo, Duke of the Archipelago (1480–1494) John III, Duke of Cleves (1490–1539) John III of Portugal (1502–1557), King of Portugal and of the Algarves John III of Sweden (1537–1592) John III Sobieski (1629–1696), King of Poland and Grand Duke of Lithuania Yohannes III of Ethiopia (c. 1824 – c. 1873), Emperor several times between 1840 and 1851 Prince Juan, Count of Montizón, Carlist pretender to the title, Juan III, King of Spain, 1861-1868 and Legitimist pretender to title, Jean III, King of France. Prince Jean, Duke of Guise, pretended to the title John III, King of the French, 1926–1940 Infante Juan, Count of Barcelona, pretended to the title Juan III, King of Spain, 1941–1977 John Ernest III, Duke of Saxe-Weimar (1664–1707) John Frederick III, Duke of Saxony (1538–1565) John William III, Duke of Saxe-Eisenach (1666–1729) Jean, Grand Duke of Luxembourg, the 3rd ruler of Luxembourg of that name
Biblical John 3, the third chapter of the Gospel of John Third Epistle of John or 3 John Ioannes III (disambiguation)