APA (7th ed.) Citation

Courant, R., Robbins, H., & Stewart, I. (1996). What is mathematics: An elementary approach to ideas and methods.

Chicago Style (17th ed.) Citation

Courant, Richard, Herbert Robbins, and Ian Stewart. What Is Mathematics: An Elementary Approach to Ideas and Methods. Oxford Univ. Press, 1996.

MLA (9th ed.) Citation

Courant, Richard, et al. What Is Mathematics: An Elementary Approach to Ideas and Methods. 1996.