Saxe-Gotha (German: Sachsen-Gotha) was one of the Saxon duchies held by the Ernestine branch of the Wettin dynasty in the former Landgraviate of Thuringia.

The duchy was established in 1640, when Duke Wilhelm von Saxe-Weimar created a subdivision for his younger brother Ernest I the Pious.

Nevertheless, Albert died in 1644, and Ernest inherited large parts of his duchy, though not the core territory around the residence at Eisenach and the Wartburg, which fell to his elder brother Wilhelm of Saxe-Weimar.

Finally in 1672 he received the major part of Saxe-Altenburg through his wife Elisabeth Sophie, after Altenburg's last duke Frederick William III had died without heirs.

After the abolition of German monarchies at the end of the First World War it became a part of the newly created state of Thuringia in 1920.