Hanns Eisler (German pronunciation: [ˈhans ˈaɪslɐ]; 6 July 1898 – 6 September 1962) was an Austrian and German composer. He is best known for composing the national anthem of East Germany, for his long artistic association with Bertolt Brecht, and for the scores he wrote for films. The Hochschule für Musik Hanns Eisler Berlin is named after him.

Johannes Eisler was born in Leipzig, Saxony, on 6 July 1898 – the third child of Rudolf Eisler and Marie Ida Fischer. His father was a philosophy professor and an atheist of Jewish descent, and his mother was Lutheran of Swabian descent. In 1901, the family moved to Vienna. His older brother Gerhart was a communist journalist, and his older sister Elfriede was a leader of the Communist Party of Germany in the 1920s. After emigrating to North America, she turned into an anti-Stalinist and testified against him and his brother before the House Un-American Activities Committee.

As his family could not afford music lessons nor a piano, Eisler had to teach himself music. At age 14, Eisler joined a socialist youth group.

In 1917, one year after Eisler graduated high school, the 18-year-old Eisler was drafted into the Austro-Hungarian Army to fight during World War I, where he served as a front-line soldier. He found this time physically demanding, due to his poor health and small stature, and was injured several times in combat.

Returning to Vienna after Austria's defeat, he studied from 1919 to 1923 under Arnold Schoenberg. Eisler was the first of Schoenberg's disciples to compose in the twelve-tone or serial technique.

Eisler married Charlotte Demant in 1920; they separated in 1934. In 1925, he moved to Berlin, which was then a hothouse of experimentation in music, theater, film, art and politics. There he became an active supporter of the Communist Party of Germany and became involved with the November Group. In 1928, he taught at the Marxist Workers' School in Berlin and his son Georg Eisler was born. His music became increasingly oriented towards political themes and, to Schoenberg's dismay, more "popular" in style with influences drawn from jazz and cabaret. At the same time, he became close with Bertolt Brecht, whose own turn towards Marxism happened at about the same time. The collaboration between the two artists lasted for the rest of Brecht's life.

In 1929, Eisler composed the song cycle Zeitungsausschnitte, Op. 11. The work is dedicated to the singer Margot Hinnenberg-Lefebre. Though not written in the twelve-tone technique, it was perhaps the forerunner of a musical art style later known as "News Items" (or perhaps better characterized as "news clippings") – musical compositions that parodied a newspaper's content and style, or that included lyrics lifted directly from newspapers, leaflets, magazines or other written media of the day. The cycle parodies a newspaper's layout and content, with the songs comprising it given titles similar to headlines. Its content reflects Eisler's socialist leanings, with lyrics memorializing the struggles of ordinary Germans subject to post–World War I hardships.

Eisler wrote music for several Brecht plays, including The Decision (Die Maßnahme) (1930), The Mother (1932) and Schweik in the Second World War (1957). They also collaborated on protest songs that celebrated, and contributed to, the political turmoil of Weimar Germany in the early 1930s. Their "Solidarity Song" became a popular militant anthem sung in street protests and public meetings throughout Europe, and their "Ballad of Paragraph 218" was the world's first song protesting laws against abortion. Brecht-Eisler songs of this period tended to look at life from "below"—from the perspective of prostitutes, hustlers, the unemployed and the working poor. From 1931 to 1932, he collaborated with Brecht and director Slatan Dudow on the working-class film Kuhle Wampe.