The House of Schleswig-Holstein-Sonderburg-Augustenburg was a branch of the dukes of Schleswig-Holstein-Sonderburg of the House of Oldenburg. The line descended from Alexander, Duke of Schleswig-Holstein-Sonderburg. Like all of the secondary lines from the Sonderburg branch, the heads of the House of Schleswig-Holstein-Sonderburg-Augustenburg were first known as Dukes of Schleswig-Holstein and Dukes of Sonderburg. The family took its name from its ancestral home, Augustenborg Palace in Augustenborg, Denmark.

Schleswig-Holstein-Sonderburg was the name of a branch line of the House of Oldenburg as well as the name of their land. It existed from 1564 until 1668 and was a titular duchy under the King of Denmark, rather than a true territorial dukedom in its own right. The seat of the duke was Sønderborg. Parts of the domain were located in Denmark, mainly on the islands of Als and Ærø and around Glücksburg, whilst other lands were part of the Holy Roman Empire, including the Ämter of Plön, Ahrensbök, and Reinfeld. As a result of various inheritance arrangements it fragmented into numerous small territories which were eventually absorbed into Greater Denmark in the 18th century.