Karl Søren Clausen (15 August 1904 – 5 December 1972) was a Danish pianist, conductor, composer and musicologist.
In addition to his work as a high school teacher in German and Music, he composed several instrumental and choral works, as well as songs.
He became increasingly involved in work with amateur choirs and school singing, and he became a very popular choir conductor, who led several choirs to many musical successes, often with his own choir arrangements, based on folk melodies.
The strong folk singing tradition that he experienced in his childhood Sønderjylland under German rule became decisively influential during his later career.
In the late 1940s he began collecting sound recordings of folk singing in marginal, rural areas of Jylland, and in the 1960s he continued this work in the isolated Faroe Islands in the North Atlantic.
Alongside teaching and collection work, Clausen also began studying the history of Danish and North German folk singing, and put folk singing into a new context, incorporating historical, religious and sociological aspects, as reflected in various articles, as well as a textbook.