APA (7th ed.) Citation

Gamma, E., Helm, R., Johnson, R., & Vlissides, J. (1995). Design patterns elements of reusable object-oriented software. Addison-Wesley.

Chicago Style (17th ed.) Citation

Gamma, Erich, Richard Helm, Ralph Johnson, and John Vlissides. Design Patterns Elements of Reusable Object-oriented Software. Boston: Addison-Wesley, 1995.

MLA (9th ed.) Citation

Gamma, Erich, et al. Design Patterns Elements of Reusable Object-oriented Software. Addison-Wesley, 1995.