- The history of keyboard music to 1700Willi Apel
- Harvard dictionary of musicWilli Apel
- Masters of the keyboardWilli Apel
- Gregorian chantWilli Apel
- The Harvard brief dictionary of musicWilli Apel
- Italian violin music of the seventeenth centuryWilli Apel
- French secular music of the late fourteenth centuryWilli Apel
- Die Notation der polyphonen Musik 900 - 1600Willi Apel
- Harvard Brief Dictionary of Music DictionaryWilli Apel
