Snell, George Davis (1903-1996) was an American geneticist who discovered the genes responsible for the rejection of tissue transplants. He shared the 1980 Nobel Prize in physiology or medicine with Jean Baptiste Gabriel Joachim Dausset and Baruj Benacerraf for related studies.

Snell received his Ph.D. degree in genetics from Harvard University in 1930. The following year he went to the University of Texas at Austin on a fellowship from the National Research Council. There he worked under renowned geneticist Hermann Joseph Muller. While studying the genetic effect on mice, Snell demonstrated for the first time that X rays could cause chromosomial changes in mammals. Snell moved to the respected Jackson Laboratory in Bar Harbor, Maine, in 1935 and remained there throughout the rest of his career.

During his first years at Jackson, Snell continued his research into X-ray related mutations. In 1944, he began studying the role of genetics in tissue transplants. With British geneticist Peter Gorer, Snell determined for the first time with certainty that genes were directly involved in histocompatibility, the compatibility between the genetic makeup of donor tissue and recipient that allows a tissue graft from the former to be accepted by the latter. They also found that, rather than a single gene being responsible, the outcome was actually determined by a group of closely related genes, which they named the Major Histocompatibility Complex (MHC). Their discovery of MHC and of its presence in the human body, as well as further findings by other scientists throughout the 1950's, made widespread organ transplantation possible. Donors and recipients could be matched to see if they were compatible.

After his retirement in the late 1960's, Snell continued to be actively involved in his field. In addition to winning the Nobel Prize, he was a recipient of the American Medical Association's Hecktoen Silver Medal, the Gregor Mendel Medal, and a career award from the National Cancer Institute.