Dorothea von Biron, Princess of Courland, Duchess of Dino, Duchess of Talleyrand and Duchess of Sagan, known as Dorothée de Courlande or Dorothée de Dino, was a Baltic German noblewoman, and the ruling Duchess of Sagan between 1845 and 1862. Her mother was Dorothea von Medem, Duchess of Courland, and although her mother's husband, Duke Peter von Biron, acknowledged her as his own, her true father may have been the Polish statesman Count Aleksander Batowski. For a long time, she accompanied the French statesman Charles Maurice de Talleyrand-Périgord; she was the separated wife of his nephew, Edmond de Talleyrand-Périgord.

The Duchy of Żagań or Duchy of Sagan was one of the duchies of Silesia ruled by the Silesian Piasts. Its capital was Żagań in Lower Silesia, the territory stretched to the town of Nowogród Bobrzański in the north and reached the Lusatian Neisse at Przewóz in the west, including two villages beyond the river.