APA (7th ed.) Citation

Willoughby, W. W. (1914). The American constitutional system: An introduction to the study of the American state. Century.

Chicago Style (17th ed.) Citation

Willoughby, Westel Woodbury. The American Constitutional System: An Introduction to the Study of the American State. New York: Century, 1914.

MLA (9th ed.) Citation

Willoughby, Westel Woodbury. The American Constitutional System: An Introduction to the Study of the American State. Century, 1914.