Theodor Heuss (German: [ˈteːodoːɐ̯ ˈhɔʏs] ^ⓘ; 31 January 1884 – 12 December 1963) was a German liberal politician who served as the first president of West Germany from 1949 to 1959. His civil demeanour and his cordial nature – something of a contrast to German nationalist traditions and the stern character of chancellor Konrad Adenauer – largely contributed to the stabilization of democracy in West Germany during the Wirtschaftswunder years. Before beginning his career as a politician, Heuss had been a political journalist. To this day, Heuss is remembered as a major representative of social liberalism in Germany.

Heuss was born in Brackenheim, a small town and wine-making community near Heilbronn in Württemberg, on the border between the historic regions of Swabia and Franconia.

He attended the Karlsgymnasium in Heilbronn, from which he graduated in 1902. This selective secondary school has since been renamed the Theodor-Heuss-Gymnasium, in honor of its famous alumnus.

Heuss studied economics, art history and political science at the universities of Munich and Berlin. He received his doctorate at Munich, with social reformer Lujo Brentano serving as his thesis adviser, in 1905. Heuss was also a student of Friedrich Naumann, a social liberal politician and theologian. On 11 April 1908, he married Elly Heuss-Knapp (1881–1952), with whom he had a son. The minister presiding over the Lutheran wedding ceremony held in Straßburg was Albert Schweitzer, a close friend of Elly.

After his studies Heuss worked as a political journalist in Berlin and from 1905 until 1912 presided over the magazine Die Hilfe ("The Aid") published by Friedrich Naumann. From 1912 to 1918, he was editor in chief of the liberal Neckarzeitung (Neckar Newspaper) in Heilbronn. In Berlin, he worked as editor for the weekly newsletter Deutsche Politik ("German Politics") and the magazine Die Deutsche Nation ("The German Nation"). With Naumann, Heuss in 1903 joined the liberal Free-minded Union, which in 1910 merged into the Progressive People's Party (Fortschrittliche Volkspartei), in which he was engaged until its dissolution in 1918.

After World War I, Heuss became a member of the left liberal German Democratic Party (Deutsche Demokratische Partei, DDP), from 1930 renamed German State Party (Deutsche Staatspartei, DStP), the political heir of the Fortschrittliche Volkspartei in 1918 and was a member of the Reichstag from 1924 to 1928 and again from 1930 to 1933. He also taught as a lecturer at the Deutsche Hochschule für Politik ("German Academy for Politics") in Berlin. From 1918 to 1924, Heuss was managing director of Deutscher Werkbund, a German association of artists, architects, designers and industrialists which became an important element in the development of modern architecture and industrial design, particularly in the later creation of the Bauhaus school of design.

During the 1920s and early 1930s, Heuss was a staunch supporter of the democratic Weimar Republic and an opponent of Adolf Hitler's Nazi Party, about which he published one of the first comprehensive analyses in 1932 with the book Hitlers Weg ("Hitler's Way"). However, on 23 March 1933, along with his four fellow DStP parliamentarians, Heuss voted in favour of the Enabling Act (Ermächtigungsgesetz), granting Chancellor Adolf Hitler quasi-dictatorial powers. He had set out to abstain, but after Heinrich Brüning indicated that with regard to the Reichskonkordat the Centre Party MPs would assent, ultimately subordinated to party discipline. Alternative views of Hermann Dietrich, Weimar Republic finance minister claim that he was part of the majority in favor of voting for the enabling law.

When Germany became a one-party state, the DStP was dissolved on 28 June 1933 and Heuss was divested of his Reichstag mandate by decree of Minister of the Interior Wilhelm Frick with effect from 8 July. He also lost his positions at the Deutsche Hochschule für Politik and at the Deutscher Werkbund. Several of his books were banned and burned during the Nazi book burnings.