Robert Ghormley Parr (born September 22, 1921) is a theoretical chemist.
He received his A. B. degree magna cum laude from Brown University in 1942 and his Ph. D. in physical chemistry from the University of Minnesota in 1947. He joined the faculty at Minnesota on receiving his Ph. D., serving in 1947-48. In 1948 he moved to the Carnegie Institute of Technology (now part of Carnegie-Mellon University) in Pittsburgh, Pennsylvania, becoming a full professor in 1957. In 1962 he moved to Johns Hopkins University in Baltimore, Maryland, and in 1974 to the University of North Carolina at Chapel Hill, where he received appointment to an endowed professorship in 1990 and where he now teaches.
Together with Rudolph Pariser, he developed a method of computing approximate molecular orbitals for pi electron systems, published in 1953. (Since an identical procedure was derived by John A. Pople the same year, it is generally referred to as the Pariser-Parr-Pople method or PPP method.) He has continued to make important advances most recently based on Density Functional Theory (DFT).