Baruj Benacerraf was a Venezuelan-American immunologist, who shared the 1980 Nobel Prize in Physiology or Medicine for the "discovery of the major histocompatibility complex genes which encode cell surface protein molecules important for the immune system's distinction between self and non-self." His colleagues and shared recipients were Jean Dausset and George Davis Snell.

The major histocompatibility complex (MHC) is a large locus on vertebrate DNA containing a set of closely linked polymorphic genes that code for cell surface proteins essential for the adaptive immune system. These cell surface proteins are called MHC molecules.