Stephen Sondheim - books

Banfield, Stephen. Sondheim's Broadway Musicals. Ann Arbor: Univ. of 
Michigan Press, 1993.
 
Gordon, Joanne. Art Ain't Easy: the Achievement of Stephen 
Sondheim. Carbondale: Southern Illinois Press, 1990. 

Gottfried, Martin. Sondheim. New York: H.N. Abrams. 1993.

Zadan, Craig. Sondheim & Co. 2nd ed. New York: Harper & Row, 
Publishers, 1986.