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: 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.