György Sándor Ligeti (pronunciation^ⓘ /ˈlɪɡəti/; Hungarian: [ˈliɡɛti ˈɟørɟ ˈʃaːndor]; 28 May 1923 – 12 June 2006) was a Hungarian composer of contemporary classical music. He has been described as "one of the most important avant-garde composers in the latter half of the twentieth century" and "one of the most innovative and influential among progressive figures of his time".

Born in Romania, he lived in the Hungarian People's Republic before emigrating to Austria in 1956. He became an Austrian citizen in 1968. In 1973 he became professor of composition at the Hochschule für Musik und Theater Hamburg, where he worked until retiring in 1989. His students included Hans Abrahamsen, Unsuk Chin and Michael Daugherty. He died in Vienna in 2006.

Restricted in his musical style by the authorities of Communist Hungary, only when he reached the West in 1956 could Ligeti fully realise his passion for avant-garde music and develop new compositional techniques. After experimenting with electronic music in Cologne, Germany, his breakthrough came with orchestral works such as Atmosphères, for which he used a technique he later dubbed micropolyphony. After writing his "anti-anti-opera" Le Grand Macabre, Ligeti shifted away from chromaticism and towards polyrhythm for his later works.

He is best known by the public through the use of his music in film soundtracks. Although he did not directly compose any film scores, excerpts of pieces composed by him were taken and adapted for film use. The sound design of Stanley Kubrick's films, particularly the music of 2001: A Space Odyssey, drew from Ligeti's work.

Ligeti was born in 1923 at Diciosânmartin (Dicsőszentmárton; renamed to Târnăveni in 1941) in Romania, to Dr. Sándor Ligeti and Dr. Ilona Somogyi. His family was Hungarian Jewish. He was the great-grandnephew of violinist Leopold Auer and second cousin of Hungarian philosopher Ágnes Heller. Some sources say he was Auer's grandnephew, rather than great-grandnephew.

Ligeti recalled that his first exposure to languages other than Hungarian came one day while listening to a conversation between Romanian-speaking town police. Before that, he didn't know that other languages existed. He moved to Cluj with his family when he was six years old. He did not return to the town of his birth until the 1990s. In 1940, Northern Transylvania became part of Hungary following the Second Vienna Award, thus Cluj became part of Hungary as well.

In 1941 Ligeti received his initial musical training at the conservatory in Kolozsvár (Cluj), and during the summers privately with Pál Kadosa in Budapest. In 1944, Ligeti's education was interrupted when he was sent to a forced labor brigade by the Horthy regime during events of the Holocaust. His brother Gábor, age 16, was deported to the Mauthausen-Gusen concentration camp and his parents were sent to Auschwitz. His mother was the only person alongside Ligeti to survive in his immediate family.

Following World War II, Ligeti returned to his studies in Budapest, graduating in 1949 from the Franz Liszt Academy of Music. He studied under Pál Kadosa, Ferenc Farkas, Zoltán Kodály and Sándor Veress. He conducted ethnomusicological research into the Hungarian folk music of Transylvania. However, after a year he returned to Franz Liszt Academy in Budapest, this time as a teacher of harmony, counterpoint, and musical analysis. He secured this position with the help of Kodály and held it from 1950 to 1956. As a young teacher, Ligeti took the unusual step of regularly attending the lectures of an older colleague, the conductor, and musicologist Lajos Bárdos, a conservative Christian whose circle represented a safe haven for Ligeti. The composer acknowledged Bárdos's help and advice in the prefaces to his two harmony textbooks (1954 and 1956). Due to the restrictions of the communist government, communications between Hungary and the West by then had become difficult, and Ligeti and other artists were effectively cut off from recent developments outside the Eastern Bloc.