Saxe-Coburg and Gotha, or Saxe-Coburg-Gotha, was an Ernestine duchy in Thuringia ruled by a branch of the House of Wettin, consisting of territories in the present-day states of Thuringia and Bavaria in Germany. It lasted from 1826 to 1918. In November 1918, Charles Edward, Duke of Saxe-Coburg and Gotha, was forced to abdicate. In 1920, the northern part of the duchy was merged with six other Thuringian free states to form the Free State of Thuringia: Saxe-Weimar-Eisenach, Saxe-Altenburg and Saxe-Meiningen, Schwarzburg-Rudolstadt and Schwarzburg-Sondershausen, as well as the People's State of Reuss. The southern part of the duchy, as southernmost of the Thuringian states, was the only one which, after a referendum, became part of the Free State of Bavaria.

The Ernestine duchies, also known as the Saxon duchies, were a group of small states whose number varied, which were largely located in the present-day German state of Thuringia and governed by dukes of the Ernestine line of the House of Wettin.