Theodor Friedrich Wilhelm Willi Kahl (18 July 1893 – 3 October 1962) was a German musicologist.
Born in Saverne ([Alsace], from 1911 Kahl studied musicology, classical philology and German literature in Freiburg im Breisgau, Munich and Bonn.
In 1919 he received his doctorate under Schiedermair in Bonn with the work Das lyrische Klavierstück zu Beginn des 19.
Jahrhunderts (Studies on the history of piano music of the 18th century) and joined the library service in the same year.
In 1928 he became library councillor at the Universitäts- und Stadtbibliothek Köln [de] and at the same time received an extraordinary professorship at the University of Cologne.