Dickey, Jerry, Sophie Treadwell: A Research and Production Sourcebook, Greenwood Press, 1997.

This book chronicles the achievements of Sophie Treadwell, including a career and biographical overview, detailed plot summaries of her plays, criticism, and an annotated bibliography.

Jones, Jennifer, "In Defense of the Woman: Sophie Treadwell's Machinal," in Modern Drama, Vol. XXXVII, No. 3, Fall 1994.

Jones highlights the similarities between Machinal and the Snyder-Gray murder trial of 1927.

Kuhns, David F., German Expressionist Theatre: The Actor and the Stage, Cambridge University Press, 1997.

Kuhns traces the powerfully stylized, anti-realistic methods of symbolic acting on the German Expressionist stage from 1916 to 1921.

Styan, J. L., Modern Drama in Theory and Practice, Vol. 3, Expressionism and Epic Theatre, Cambridge University Press, 1981.

This book traces expressionism from German through American playwrights, including Eugene O'Neill, Thornton Wilder, and Sean O'Casey.