APA (7th ed.) Citation

Courant, R., & Robbins, H. (1941). What is mathematics? An elementary approach to ideas and methods / by R. Courant and H. Robbins. O.U.P..

Chicago Style (17th ed.) Citation

Courant, Richard, and H. Robbins. What Is Mathematics? An Elementary Approach to Ideas and Methods / by R. Courant and H. Robbins. O.U.P., 1941.

MLA (9th ed.) Citation

Courant, Richard, and H. Robbins. What Is Mathematics? An Elementary Approach to Ideas and Methods / by R. Courant and H. Robbins. O.U.P., 1941.

Warning: These citations may not always be 100% accurate.