Iannis Xenakis (born 29 May 1922, Brăila, Romania - died 4 February 2001, Paris, France) was a Romanian-born Greek-French composer, music theorist, architect and engineer. Was married to Françoise Xenakis.

He is regarded as one of the most radical and important composers of the twentieth century. He formulated a theory of stochastic music in the early 1950's, and in late 1954 he was accepted as a member of the Groupe De Recherche De Musique Concrète. He later joined Groupe De Recherches Musicales. He pioneered the use of computers for musical composition in 1961. As an architect, he worked with Le Corbusier and designed the Philips Pavilion for the Brussels World's Fair in 1958. In 1963, he published Musique Formelles, a collection of his articles relating music, architecture, and mathematics. In 1972, he founded CEMAMu (Centre d'Etudes de Mathématique et Automatique Musicales) in Issy-les-Moulineaux, just outside of Paris. He has composed for a wide range of instrumental ensembles and solos, and his 'polytopes', sound and light spectacles, have been performed in a number of localities, including: Persepolis (1971), Paris (1972), Mycénes (1978) and again in Paris (1978).