Augustus 'the Younger' Duke of Brunswick-Lüneburg
- Born: 10 Apr 1579, Dannenburg, Lüchow-Dannenberg, Niedersachsen, Germany
- Marriage: Unknown
- Died: 17 Sep 1666, Wolfenbüttel, Niedersachsen, Germany at age 87
Augustus, called the Younger, was duke of Brunswick-Lüneburg. In the estate division of the House of Welf of 1635, he received the Principality of Wolfenbüttel.
Augustus was the seventh child of Henry, Duke of Brunswick-Lüneburg. After complicated negotiations with his family members and an intervention by Emperor Ferdinand II, it was agreed that he should inherit Wolfenbüttel, whose last ruler had died in 1634. Because of the Thirty Years' War, he could not move into his residence until 1644. Augustus instituted a number of government reforms, and founded the Bibliotheca Augusta, a large library, in Wolfenbüttel. Under the pseudonym Gustavus Selenus, he wrote a book on chess in 1616, Chess or the King's game, and on cryptography in 1624: Cryptomenytices et Cryptographiae libri IX. The pseudonym is a cryptic reference to his name, Gustavus anagrams (with U=V) to Augustus, the surname is a play on the Greek goddess of the moon (Selene). The book on cryptography is largely based on earlier work by Trithemius.
Augustus was succeeded by his three sons, Rudolph Augustus, Anthony Ulrich, and Ferdinand Albert.