The Constitution of the German Reich, usually known as the Weimar Constitution, was the constitution that governed Germany during the Weimar Republic era (1919–1933). The constitution declared Germany to be a democratic parliamentary republic with a legislature elected under proportional representation. Universal suffrage was established, with a minimum voting age of 20. The constitution technically remained in effect throughout the Nazi era from 1933 to 1945 as well as during the Allied occupation of Germany from 1945 to 1949, though practically it had been repealed by the Enabling Act of 1933 and thus its various provisions and protections went unenforced for the duration of Nazi rule, and after World War II, the power of the Allied Control Council and four occupying powers once again stood above the provisions of the constitution.

The Weimar Republic, officially known as the German Reich, was a historical period of Germany from 9 November 1918 to 23 March 1933, during which it was a constitutional federal republic for the first time in history; hence it is also referred to, and unofficially proclaimed itself, as the German Republic. The period's informal name is derived from the city of Weimar, which hosted the constituent assembly that established its government. In English, the republic was usually simply called "Germany", with "Weimar Republic" not commonly used until the 1930s.