APA (7th ed.) Citation

Lewis, C. S. (1950). The Screwtape Letters: C. S. Lewis. Macmillan.

Chicago Style (17th ed.) Citation

Lewis, Clive S. The Screwtape Letters: C. S. Lewis. New York: Macmillan, 1950.

MLA (8th ed.) Citation

Lewis, Clive S. The Screwtape Letters: C. S. Lewis. Macmillan, 1950.