APA (7th ed.) Citation

Hardon, J. A. (1971). Christianity in the twentieth century. Doubleday.

Chicago Style (17th ed.) Citation

Hardon, John A. Christianity in the Twentieth Century. Garden City, N.Y: Doubleday, 1971.

MLA (9th ed.) Citation

Hardon, John A. Christianity in the Twentieth Century. Doubleday, 1971.