Treitler's major work is in Medieval and Renaissance music, particularly in Gregorian chant and the earliest polyphony. He also published a series of essays exploring historiography in music history, which were collected, with other works on music history and theory, in Music and the Historical Imagination. He revised Oliver Strunk's Source Readings in Music History in 1998.
"The Early History of Music Writing in the West." Journal of the American Musicological Society, vol. 35, no. 2 (Summer 1982), pp.237–279
"Reading and Singing: On the Genesis of Occidental Music-Writing." Early Music History, vol. 4 (1984), pp.135–208
"The 'Unwritten' and 'Written Transmission' of Medieval Chant and the Start-Up of Musical Notation." The Journal of Musicology, vol. 10, no. 2 (Spring 1992), pp.131–191