William IV (German: Wilhelm) called William the Younger (German: Wilhelm der Jüngere, c. 1425 – 7 July 1503) was duke of Brunswick-Lüneburg and ruled over the Wolfenbüttel and Göttingen principalities.

The eldest son of William the Victorious, Duke of Brunswick-Lüneburg, he was given the Principality of Göttingen by his father in 1473.

In 1491, William gave the Principality of Wolfenbüttel including Calenberg to his sons, and kept only Göttingen to himself.

In 1495 he resigned as prince of Göttingen in favour of his son Eric I in return for an appanage.

William married Elizabeth (c. 1438 – 7 September 1520), daughter of Bodo VII, Count of Stolberg-Wernigerode.