Rosalyn Sussman Yalow (July 19, 1921 – May 30, 2011) was an American medical physicist, and a co-winner of the 1977 Nobel Prize in Physiology or Medicine (together with Roger Guillemin and Andrew Schally) for development of the radioimmunoassay (RIA) technique. She was the second American woman to be awarded the Nobel Prize Physiology or Medicine after Gerty Cori.