APA (7th ed.) Citation

Asimov, I., Greenberg, M. H., & Waugh, C. G. (1988). Encounters. Headline.

Chicago Style (17th ed.) Citation

Asimov, Isaac, Martin Harry Greenberg, and Charles G. Waugh. Encounters. London [England]: Headline, 1988.

MLA (9th ed.) Citation

Asimov, Isaac, et al. Encounters. Headline, 1988.