Richman, Kitty. "Chimpanzees." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 5th ed. Vol. 2. Farmington Hills, MI: Gale, 2014. 905-910. Gale Virtual Reference Library. Web. 20 May 2015.

Fouts, Roger, and Deborah Fouts. "Chimpanzees." Encyclopedia of Animal Rights and Animal Welfare. Ed. Marc Bekoff and Carron A. Meaney. Westport, CT: Greenwood Press, 1998. 105-107. Gale Virtual Reference Library. Web. 20 May 2015.

Overview page in the Opposing Viewpoints in Context database providing links to background essays, pro/con essays, statistics, news articles, etc.

Regan, Tom, et al. "Animal Rights." Encyclopedia of Animal Rights and Animal Welfare. Ed. Marc Bekoff and Carron A. Meaney. Westport, CT: Greenwood Press, 1998. 42-50. Gale Virtual Reference Library. Web. 20 May 2015.

"Animal Liberation Front (ALF)." Extremist Groups: Information for Students. Vol. 1. Detroit: Gale, 2006. 131-138. Gale Virtual Reference Library. Web. 20 May 2015.

Waskey, Andrew J. "Interspecies Communication." Encyclopedia of Anthropology. Ed. H. James Birx. Vol. 2. Thousand Oaks, CA: SAGE Reference, 2006. 533. Gale Virtual Reference Library. Web. 20 May 2015.

Jensvold, Mary Lee, and Lori K. Sheeran. "Ape Cognition." Encyclopedia of Anthropology. Ed. H. James Birx. Vol. 1. Thousand Oaks, CA: SAGE Reference, 2006. 207-212. Gale Virtual Reference Library. Web. 20 May 2015.

Paciulli, Lisa M., and Jacqueline L. Hagen. "Ape Language." Encyclopedia of Anthropology. Ed. H. James Birx. Vol. 1. Thousand Oaks, CA: SAGE Reference, 2006. 213-214. Gale Virtual Reference Library. Web. 20 May 2015.