APA (7th ed.) Citation

Turtledove, H. (1990). A world of difference. Ballantine Books.

Chicago Style (17th ed.) Citation

Turtledove, Harry. A World of Difference. New York: Ballantine Books, 1990.

MLA (8th ed.) Citation

Turtledove, Harry. A World of Difference. Ballantine Books, 1990.