Robert Magnus Martinson (May 19, 1927 – August 11, 1979) was an American sociologist, whose 1974 study "What Works?", concerning the shortcomings of existing prisoner rehabilitation programs, was highly influential, creating what became known as the "nothing works" doctrine.
His later studies were more optimistic, but less influential at the time.
He served as chairman of the Sociology Department at the City College of New York, and then founded the Center for Knowledge in Criminal Justice Planning.