Charles III (born 1948) is King of the United Kingdom and 14 other Commonwealth realms.

Charles III may also refer to:

• Charles III of the Carolingian Empire ("Charles the Fat") (839–888)
• Charles III of West Francia ("Charles the Simple") (879–929)
• Charles III of Anjou (1290–1325)
• Charles III of Alençon (1337–1375)
• Charles III of Naples (1345–1386)
• Charles III of Navarre (1361–1425)
• Charles III, Duke of Savoy (1486–1553)
• Charles III, Duke of Bourbon (1490–1527)
• Charles III, Duke of Lorraine (1543–1608)
• Charles III, Prince of Guéméné (1655–1727)
• Charles III Philip, Elector Palatine (1661–1742)
• Charles III William, Margrave of Baden-Durlach (1679–1738)
• Charles III of Hungary (Charles VI, Holy Roman Emperor) (1685–1740)
• Charles III of Spain (1716–1788)
  • The name Charles III of Spain was also used by Charles VI, Holy Roman Emperor (1685–1740) during the War of the Spanish Succession, c. 1705–1713
• Charles III John of Norway (Charles XIV John of Sweden and Norway) (1763–1844)
• Charles Albert III, Prince of Hohenlohe-Waldenburg-Schillingsfürst (1776–1843)
• Charles III, Prince of Monaco (1818–1889)
• Charles Egon III, Prince of Fürstenberg (1820–1892)
• Charles III, Duke of Parma (1823–1854)
• Charles III of Bohemia (Charles I of Austria) (1887–1922)

• Charles Edward Stuart (1720–1788), Stuart pretender who styled himself Charles III
• King Charles III (play), a 2014 play by Mike Bartlett, about the British king (released when he was Prince of Wales)
• King Charles III (film), a 2017 adaptation of the play
• Charles III (album), by organist Charles Earland

• King Charles (disambiguation)
• Order of Charles III, established by Charles III of Spain
• Carlos III (disambiguation)