William III or William the Third may refer to:
Kings William III of Sicily () William III of England and Ireland or William III of Orange or William II of Scotland (1650–1702) William III of the Netherlands and Luxembourg (1817–1890)
Nobles
William III, Duke of Aquitaine (913–963) William II, Count of Provence, also numbered William III of Provence, (late 980s–1018) William III, Count of Toulouse, also styled William III of Provence (–1037) William III of Provence (died after 1037) William III of Weimar (died 1039) William III, Marquess of Montferrat (–1042) William III, Lord of Montpellier (died 1058) William V, Count of Angoulême, also known as William Taillefer III (1084–1118/20) William III, Count of Burgundy (–1127) William III of Forcalquier (died 1129) William III of Mâcon (1088–1156) William III, Count of Nevers (–1161) William III, Count of Ponthieu (–1172) William III, Count of Jülich () William II of Flanders, also styled William III of Dampierre (1224–1251) William de Cantilupe (died 1254) William III of Baux (died 1257) William III of Cagliari () William III of Geneva (1280-1320) William I, Count of Hainaut or William III of Holland (–1337) William III, Earl of Ross, known as , 5th Earl of Ross (died 1372) William I, Duke of Bavaria or William III of Hainaut (1330–1389) William III, Duke of Bavaria (1375–1435) William III of Isenburg-Wied () William III, Princely count of Henneberg-Schleusingen (1434–1480) William III, Landgrave of Thuringia (1425–1482) William III, Landgrave of Hesse (1471–1500)
Horses William the Third (horse)
See also Guillaume III (disambiguation), the French equivalent of William III King William (disambiguation) Prince William (disambiguation) List of people with given name William#Royalty and nobility