He is the author of Jewish Liturgy: A Comprehensive History. Originally published in German in 1913, this book was updated in a number of subsequent Hebrew editions. The latest Hebrew edition was translated into English by Raymond P. Scheindlin, and published by the Jewish Publication Society in 1993.
This work covers the entire range of Jewish liturgical development, beginning with the early cornerstones of the siddur; through the evolution of the medieval piyyut tradition; to modern prayerbook reform in Germany and the United States. It is the most thorough academic study of the Jewish liturgy ever written.