APA (7th ed.) Citation

Gaarder, J., & Moller, P. (1994). Sophie's world: A novel about the history of philosophy. Phoenix.

Chicago Style (17th ed.) Citation

Gaarder, Jostein, and Paulette Moller. Sophie's World: A Novel About the History of Philosophy. London: Phoenix, 1994.

MLA (9th ed.) Citation

Gaarder, Jostein, and Paulette Moller. Sophie's World: A Novel About the History of Philosophy. Phoenix, 1994.