Karl-Birger Blomdahl (19 October 1916 – 14 June 1968) was a Swedish composer and conductor born in Växjö. He was educated in biochemistry, but was primarily active in music and by his experimental compositions he became one of the big names in Swedish modernism. His teachers included Hilding Rosenberg. He died in Kungsängen, Stockholm.

His third symphony, Facettes – a work in one subdivided movement as a twelve-tone variation-form piece – from 1950 is a major contribution to the repertoire. In 1959 he composed the opera Aniara based on the poem by Harry Martinson. His output of compositions also includes concertos for violin and viola, a chamber concerto for piano, winds and percussion, at least one other opera (Herr von Hancken), and much chamber music, including a trio for clarinet, cello and piano.