Malcolm L. McCallum (born December 26, 1968) is an American environmental scientist, conservationist, herpetologist, and natural historian and is known for his work on the Holocene Extinction. He is also a co-founder of the herpetology journal, Herpetological Conservation and Biology. He is a key figure in amphibian biology and his research has produced numerous landmark studies. His work has been covered by David Attenborough, Discover Magazine, and other media outlets.