The Duchy of Oels or Duchy of Oleśnica was one of the duchies of Silesia with its capital in Oleśnica in Lower Silesia, Poland. Initially ruled by the Silesian Piasts, it was acquired by the Münsterberg (Ziębice) dukes of the Podiebrad family from 1495 and was inherited by the House of Württemberg in 1649. Conquered by Prussia in 1742, it was enfeoffed to the Welf dukes of Brunswick-Lüneburg from 1792 until its dissolution in 1884.

The Duchies of Silesia were the more than twenty divisions of the region of Silesia formed between the 12th and 14th centuries by the breakup of the Duchy of Silesia, then part of the Kingdom of Poland. In 1335, the duchies were ceded to the Kingdom of Bohemia under the Treaty of Trentschin. Thereafter until 1742, Silesia was one of the Bohemian crown lands and lay within the Holy Roman Empire. Most of Silesia was annexed by the King of Prussia under the Treaty of Berlin in 1742. Only the Duchy of Teschen, the Duchy of Troppau and the Duchy of Nysa remained under the control of the Bohemian crown and as such were known as the Duchy of Upper and Lower Silesia until 1918.