APA (7th ed.) Citation

Phelps, W. L. (1920). The twentieth century theatre: Observations on the contemporary English and American stage. MacMillan.

Chicago Style (17th ed.) Citation

Phelps, William Lyon. The Twentieth Century Theatre: Observations on the Contemporary English and American Stage. New York: MacMillan, 1920.

MLA (9th ed.) Citation

Phelps, William Lyon. The Twentieth Century Theatre: Observations on the Contemporary English and American Stage. MacMillan, 1920.