Karl Gustav Fellerer (7 July 1902 – 7 January 1984) was a German musicologist. His works include more than 600 scientific publications on catholic church music, Italian music from 1600 to the beginning of the 20th century, and music history of the 19th century. He wrote monographs on Palestrina, Handel, Mozart, and Max Bruch and was editor of several musical journals. He published the Kirchenmusikalisches Jahrbuch (Church Music Almanac) for 46 years, from 1930 until 1976. Fellerer was president of several musicology societies, including 16 years of the Joseph Haas Society.