Ernest Günther, Duke of Schleswig-Holstein-Sonderburg-Augustenburg (d. 1689)
Ernest Günther of Schleswig-Holstein-Sonderburg-Augustenburg (14 October 1609 – 18 January 1689) was a Duke of Schleswig-Holstein of its Sonderborg line. He was the first to have his ducal seat in Augustenborg Palace, which he built and named in honor of his wife. He ruled from 1647 until his death in 1689.

He was third son of Alexander, Duke of Schleswig-Holstein-Sonderburg and his wife Countess Dorothea of Schwarzburg-Sondershausen.