Robert J. Plomin (born 1948 in Chicago, Illinois) is an American psychologist best known for his work in twin studies and behavior genetics.
Plomin 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 under personality psychologist Arnold Buss. He then worked at the Institute for Behavioral 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 the Institute of Psychiatry (King's College London). He has been president of the Behavior Genetics Association, which in 2002 awarded him the Dobzhansky Memorial Award for a Lifetime of Outstanding Scholarship in Behavior Genetics. He was awarded the William James Fellow Award by the Association for Psychological Science in 2004 and the 2011 Lifetime Achievement Award of the International Society for Intelligence Research. Plomin was ranked among the 100 most eminent psychologists in the history of science (in Review of General Psychology, 2002).