Pierre Louis Joseph Boulez (French: [pjɛʁ lwi ʒozεf bulɛz]; 26 March 1925 – 5 January 2016) was a French composer, conductor and writer, and the founder of several musical institutions. He was one of the dominant figures of post-war Western classical music.

Born in Montbrison in the Loire department of France, the son of an engineer, Boulez studied at the Conservatoire de Paris with Olivier Messiaen, and privately with Andrée Vaurabourg and René Leibowitz. He began his professional career in the late 1940s as music director of the Renaud-Barrault theatre company in Paris. He was a leading figure in avant-garde music, playing an important role in the development of integral serialism (in the 1950s), controlled chance music (in the 1960s) and the electronic transformation of instrumental music in real time (from the 1970s onwards). His tendency to revise earlier compositions meant that his body of work was relatively small, but it included pieces regarded by many as landmarks of twentieth-century music, such as Le Marteau sans maître, Pli selon pli and Répons. His uncompromising commitment to modernism and the trenchant, polemical tone in which he expressed his views on music led some to criticise him as a dogmatist.

Boulez was also one of the most prominent conductors of his generation. In a career lasting more than sixty years, he was music director of the New York Philharmonic and the Ensemble intercontemporain, chief conductor of the BBC Symphony Orchestra and principal guest conductor of the Chicago Symphony Orchestra and the Cleveland Orchestra. He made frequent appearances with many other orchestras, including the Vienna Philharmonic, the Berlin Philharmonic and the London Symphony Orchestra. He was known for his performances of the music of the first half of the twentieth century—including Debussy and Ravel, Stravinsky and Bartók, and the Second Viennese School—as well as that of his contemporaries, such as Ligeti, Berio and Carter. His work in the opera house included the Jahrhundertring—the production of Wagner's Ring cycle for the centenary of the Bayreuth Festival—and the world premiere of the three-act version of Alban Berg's Lulu. His recorded legacy is extensive.

He founded several musical institutions: the Domaine musical, Institut de recherche et coordination acoustique/musique (IRCAM), Ensemble intercontemporain and Cité de la Musique in Paris, and the Lucerne Festival Academy in Switzerland.