Free State of Coburg in the context of Charles Edward, Duke of Saxe-Coburg and Gotha

Saxe-Coburg and Gotha (German: Sachsen-Coburg und Gotha), or Saxe-Coburg-Gotha (German: Sachsen-Coburg-Gotha [ˈzaksn̩ ˈkoːbʊʁk ˈɡoːta]), 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 (since 1918 the Free State of Gotha; culturally and linguistically Thuringian) was merged with six other Thuringian free states to form the Free State of Thuringia: Saxe-Weimar-Eisenach (until 1918 a grand duchy), Saxe-Altenburg and Saxe-Meiningen (until 1918 duchies), Schwarzburg-Rudolstadt and Schwarzburg-Sondershausen (until 1918 principalities), as well as the People's State of Reuss (until 1918 the principalities of Reuss-Gera and Reuss-Greiz). The southern part of the duchy (since 1918 the Free State of Coburg; culturally and linguistically Franconian), as southernmost of the Thuringian states, was the only one which, after a referendum, became part of the Free State of Bavaria.

The name Saxe-Coburg-Gotha also refers to the family of the ruling House of Saxe-Coburg and Gotha, which played many varied roles in the dynastic and political history of Europe in the 19th and 20th centuries. In the early part of the 20th century, before the First World War, it was the family of the sovereigns of the United Kingdom, Belgium, Portugal, Bulgaria, and Saxe-Coburg-Gotha. In 1910, the Portuguese king was deposed, and the same thing occurred in Saxe-Coburg-Gotha in 1918 and in Bulgaria in 1946 (although effective control had already ceased two years prior due to a coup). As of 2025, a branch of the family still reigns in Belgium, and while the British line still technically exists up to the present day, it now uses the name Windsor due to a proclamation issued by King George V in 1917. The former Tsar of Bulgaria, Simeon II (reigned 1943–46), kept his surname while serving as the Prime Minister of Bulgaria from 2001 to 2005.

The State of Thuringia (German: Land Thüringen, [lant ˈtyːʁɪŋən]) was a state of the Weimar Republic from 1920 to 1933, of Nazi Germany from 1933 to 1945 and of East Germany from 1949 to 1952. Following German reunification, the renamed Free State of Thuringia became a member state of the Federal Republic of Germany in 1990.

The State of Thuringia formed in the aftermath of World War I and the German revolution of 1918–1919. The eight small Thuringian states that had been part of the German Empire drove out their ruling royal houses and adopted republican constitutions in 1918–1919. On 1 May 1920, all except Coburg, which chose to become part of Bavaria, combined to create the State of Thuringia within the Weimar Republic.