Karl-Birger Blomdahl (born October 19, 1916, Växjö, Sweden - died June 14, 1968, Kungsängen, Sweden) was a Swedish composer and conductor.
He first wanted to study biochemistry and therefore came to Stockholm. Soon his interest in music became predominant. In 1935 he started taking lessons in musical theory and composition from Hilding Rosenberg. Soon he became the informal leader among the circle of friends called the Monday Group (other composers included Claude Loyola Allgén, Sven‐Erik Bäck, Sven-Eric Johanson, Hans Leygraf and Ingvar Lidholm) in which new music and new techniques of composition were put under the microscope. They took as their starting point the “neue Sachlichkeit“ of Hindemith’s Unterweisung im Tonsatz. His music later moved towards the Second Viennese School and further marching towards the more experimental domains. During the fifties and sixties, Blomdahl was one of the most influential Swedish composers and music administrators. Apart from his radical work as a composer, he was working as a private composition teacher towards the end of the 1940's, between 1960 and 1964 he was Professor of Composition at the Academy, he was Secretary of the Swedish Section of the ISCM 1947-1956 and Chairman of Fylkingen 1949-1954. After a few years as consultant, he became head of the Music Broadcasting Department of the Swedish Broadcasting Corporation in 1965.
His notable works include: Pastoralsvit (1948), Symphony No. 3 "Facettes", I Speglarnas Sal (1952), the ballets Sisyphos (1954) and Minotaurus (1957), and the operas Aniara (1959) and Herr von Hancken (1964). The latter which has still never been released on record, only a TV & radio performance in September of 1965.