APA (7th ed.) Citation

Courant, R., & Robbins, H. (1941). What is mathematics: An elementary approach to ideas and methods. Oxford university press.

Chicago Style (17th ed.) Citation

Courant, Richard, and Herbert Robbins. What Is Mathematics: An Elementary Approach to Ideas and Methods. London ; New York: Oxford university press, 1941.

MLA (9th ed.) Citation

Courant, Richard, and Herbert Robbins. What Is Mathematics: An Elementary Approach to Ideas and Methods. Oxford university press, 1941.