The Free State of Anhalt (German: Freistaat Anhalt) was a state of the Weimar Republic from 1919 to 1933 and of Nazi Germany from 1933 to 1945. It is today part of the German state of Saxony-Anhalt.

The Duchy of Anhalt became the Free State of Anhalt during the German revolution of 1918–1919. The ruling House of Ascania abdicated peacefully, and a constitutional assembly was elected which drew up a republican constitution for Anhalt as a member state of the Weimar Republic. Throughout most of the Republic's fourteen-year life, the Social Democratic Party was the dominant political force in Anhalt, and it saw relatively little of the violence that flared up in other parts of Weimar-era Germany. Anhalt was nevertheless the first Weimar state to elect a local parliament with a Nazi majority (May 1932).

Anhalt became part of the Nazi Gau Magdeburg-Anhalt in 1933. Late in World War II, Dessau, Anhalt's capital city, was almost completely destroyed by Allied bombing, as was the smaller city of Zerbst. The region was ceded to Russian occupation forces on 1 July 1945, and three weeks later the Free State of Anhalt formally ceased to exist when it was merged into the Soviet-administered state of Saxony-Anhalt. It was dissolved in 1952 but re-created in 1990 after the reunification of Germany.

The Duchy of Anhalt was formed in 1863 when the Duchy of Anhalt-Bernburg united with the Duchy of Anhalt-Dessau under Duke Leopold IV of Dessau. The Duchy, a member of the German Confederation, fought on the Prussian side in the 1866 Austro-Prussian War and became part of the Prussian-dominated North German Confederation in 1866 and of the German Empire in 1871.

Under the Constitution of the German Empire, the Duchy of Anhalt elected two members to the Reichstag under universal manhood suffrage and appointed one member to the Bundesrat. Anhalt had a local parliament, the Landtag, in Dessau. Its members were elected on the basis of census tax provisions which excluded poorer citizens or reduced the weight of their votes. In spite of the franchise inequality, relations between workers and the middle and upper classes were relatively good compared to other parts of the Empire. During the reign of Duke Friedrich II (1904–1918), the House of Ascania kept a relatively low profile, did not maintain a lavish court and was not involved in day-to day-politics, all qualities which helped its standing among Anhalt's working class.

As was the case before 1914, the labor situation in Anhalt during the war was quieter than in Germany as a whole. At the national level, the radical anti-war faction of the Social Democratic Party (SPD) split off to form the Independent Social Democrats (USPD) in April 1917 and went on to lead the massive strike of January 1918, but in Anhalt there was still only one very small local chapter of the USPD when the German revolution broke out in November 1918. The SPD was also able to engage successfully in local politics. It sent representatives to the Landtag for the first time in 1902, and in February 1918 it backed the liberal Fritz Hesse [de] in his successful campaign for mayor of Dessau against the conservative Ernst von Ebeling.

Duke Friedrich avoided making chauvinistic statements or patriotic calls to persevere in the face of the adversity of the war years. He was known instead for the work he and the ducal family did to try to relieve the problems caused by food shortages. Friedrich died childless in April 1918 and was succeeded by his brother Eduard, who died on 13 September. Since Eduard's son Joachim Ernst was still a minor, his uncle Aribert became prince regent.

On 6 November, when the German revolution of 1918–1919 had already swept over much of Germany, Anhalt's National Liberal and SPD leaders asked Prince Regent Aribert to replace the conservative state minister Ernst von Laue with Max Gutknecht [de] and to democratize local elections. Aribert installed Gutknecht on 3 November, and the State Ministry, formerly just one person, was expanded to seven.