Berlioz, Louis-Hector(lwē ĕktôr` bĕrlyôz`), 1803–69, French romantic composer. He abandoned medical study to enter the Paris Conservatory as a composition student. In 1830 his Symphonie fantastique was first performed in Paris, marking a bold new development in program music. This work, with its recurring basic theme, departed from traditional symphonies in its loose form and highly emotional, personal style. That same year Berlioz won the coveted Prix de Rome. During the next decade in Paris he wrote the symphonies Harold in Italy and Romeo and Juliet, the opera Benvenuto Cellini, and a requiem. In 1842–43 he conducted concerts in Germany, Austria, England, and Russia. His outstanding "concert opera" The Damnation of Faust (1846) met with failure in his lifetime but is now considered a masterpiece. Another dramatic work is the gigantic opera The Trojans, completed in 1858 but not performed in its entirety until 1890. It was successfully revived after 1920. The nonliturgical oratorio The Childhood of Christ, for which he also wrote the text, was completed in 1854, and it was performed with great success for almost a century.
Some of Berlioz's works are scored for large numbers of instruments, not only for volume but for richness of tone color even in delicate passages. His ideas of orchestration influenced many later composers. A passionate and impetuous man, Berlioz had several love affairs and was twice married, first to Harriet Smithson, an Irish actress. He was librarian at the Paris Conservatory and an incisive, witty, and urbane author whose writings include music criticism, essays on the arts, memoirs (tr. 1969; rev. ed., 2002), and the amusing Evenings with the Orchestra (tr. 1956). His treatise on instrumentation (1843) was widely recognized as a standard text.
See his letters, ed. by J. Barzun (1954); biographies by J. H. Elliot (rev. ed. 1967), J. Barzun (2 vol., 3d ed. 1969), and D. Cairns (2 vol., 2000); studies by E. Newman (1910, repr. 1969), T. S. Wotton (1935, repr. 1969), B. Primmer (1973), and K. Holoman (1990).