Frederick William I () may refer to:
Frederick William I, Duke of Saxe-Weimar (1562–1602) Frederick William, the Great Elector, of Brandenburg-Prussia (1620–1688) Frederick William I, Duke of Schleswig-Holstein-Sonderburg-Beck (1682–1719) Frederick William I of Prussia (1688–1740) Frederick William, Elector of Hesse (1802–1875)
See also Frederick William (disambiguation) Friedrich Wilhelm (disambiguation)