Willi Apel (October 10, 1893, Konitz (Chojnice) - March 14, 1988) was a Prussia-born American musicologist.
Apel studied mathematics from 1912 to 1914, and then again after World War I from 1918 to 1922, in various universities in Germany. Throughout his studies, he had an interest in music and taught piano lessons. He then turned to music full time, and essentially taught himself about musicology. He received his PhD in 1936 in Berlin, and promptly immigrated to the US. He taught at Harvard from 1938 to 1942, but moved on to spend twenty years at Indiana University beginning in 1950.