René Leibowitz (French: [ʁəne lɛbɔwits]; 17 February 1913 – 29 August 1972) was a Polish, later naturalised French, composer, conductor, music theorist and teacher. He was historically significant in promoting the music of the Second Viennese School in Paris after the Second World War, and teaching a new generation of serialist composers.

Leibowitz remained firmly committed to the musical aesthetic of Arnold Schoenberg, and was to some extent sidelined among the French avant-garde in the 1950s, when, under the influence of Leibowitz's former student, Pierre Boulez and others, the music of Schoenberg's pupil Anton Webern was adopted as the orthodox model by younger composers.

Although his compositional ideas remained strictly serialist, as a conductor Leibowitz had broad sympathies, performing works by composers as diverse as Gluck, Beethoven, Brahms, Offenbach and Ravel, and his repertory extended to include pieces by Gershwin, Puccini, Sullivan and Johann Strauss.