The Duchy of Saxe-Weimar-Eisenach (German: Herzogtum Sachsen-Weimar-Eisenach) was created in 1809 when the Ernestine duchies of Saxe-Weimar and Saxe-Eisenach were formally joined into one state. The two duchies had shared the same ruler since 1741, which is when the Saxe-Eisenach line had died out. It became a Grand Duchy in 1815.
In 1877, the Grand Duchy of Saxe-Weimar-Eisenach officially became the Grand Duchy of Saxony (German: Großherzogtum Sachsen), but this name was not often used. The Grand Duchy was abolished in 1918 with the other German monarchies, and the state joined others to form the new state of Thuringia in the Weimar Republic.
The Grand Dukes full title was Grand Duke of Saxe-Weimar-Eisenach, Landgrave in Thuringia, Margrave of Meißen, Princely Count of Henneberg, Lord of Blankenhayn, Neustadt and Tautenburg.