APA (7th ed.) Citation

Facts on File, Inc, & Drexel, J. (1991). The facts on file encyclopedia of the 20th century. Facts on File.

Chicago Style (17th ed.) Citation

Facts on File, Inc, and John Drexel. The Facts on File Encyclopedia of the 20th Century. New York: Facts on File, 1991.

MLA (9th ed.) Citation

Facts on File, Inc, and John Drexel. The Facts on File Encyclopedia of the 20th Century. Facts on File, 1991.