Mark Eden Horowitz is Senior Music Specialist in the music division of the Library of Congress where he has been an archivist or co-archivist for the papers of Jerome Kern, Oscar Hammerstein II, Richard Rodgers, Vernon Duke, Cole Porter, Frederick Loewe, Alan Jay Lerner, Leonard Bernstein and others. He is the author of the award-winning Sondheim on Music and served as the contributing editor for The Sondheim Review for ten years. He has taught the history of musical theatre at Georgetown and Catholic University.