Robert Plomin is an American psychologist best known for his work in twin studies and behavior genetics. Plomin has made two of the most important discoveries in that field. First, he has shown the importance of non-shared environment, a term that he coined to refer to the environmental reasons why children growing up in the same family are so different. Second, he has shown that many environmental measures in psychology show genetic influence and that genetic factors can mediate associations between environmental measures and developmental outcomes.

He earned a B.A. in Psychology from DePaul University in 1970 and a Ph.D. in Psychology in 1974 from the University of Texas, Austin. He then worked at the Institute for Behavioural Genetics at the University of Colorado at Boulder. From 1986 until 1994 he worked at Pennsylvania State University studying elderly twins reared apart and twins reared together to study aging and is currently at King's College London, Institute of Psychiatry.

Plomin is currently conducting the Twins Early Development Study (TEDS) of all twins born in England from 1994 to 1996, focusing on developmental delays in early childhood and their association with behavioural problems.

He has been president of the Behavior Genetics Association. In 1994 he was one of 52 signatories on "Mainstream Science on Intelligence," an editorial written by Linda Gottfredson and published in the Wall Street Journal, which defended the findings on race and intelligence in The Bell Curve.

His most recent books are Behavioral Genetics in the Postgenomic Era (Washington, DC: APA Books, 2003) and Behavioral Genetics (4th edition, New York: Worth Publishers, 2001).