Henri Pousseur (23 June 1929 – 6 March 2009) was a Belgian composer, teacher, and music theorist.
Pousseur was born in Malmedy and studied at the Academies of Music in Liège and in Brussels from 1947 to 1952, where he joined the group called Variations associated with Pierre Froidebise. It was in this group that he first became familiar with the music of Anton Webern and other 20th-century composers. During his period of military service in 1952–53 at Malines he maintained close contact with André Souris. He encountered Pierre Boulez in 1951 at Royaumont, and this contact inspired his Trois chants sacrés, composed that same year. In 1953 he met Karlheinz Stockhausen, and in 1956 Luciano Berio (Decroupet 2009). A less-well-known influence from his early years was the powerful impression of listening to the music of Anton Bruckner, and he maintained a life-long interest in medieval and Renaissance music, as well as in extra-European music and their practices (Bartholomée 2009, 68)