Pyotr Borisovich Gannushkin (Russian: Пётр Бори́сович Га́ннушкин; March 8, 1875 – February 23, 1933) was a Russian psychiatrist who developed one of the first theories of psychopathies known today as personality disorders. He was a student of Sergei Korsakoff and Vladimir Serbsky. Not only did he manage to delineate certain organizational tasks of social psychiatry, but he also clearly formulated the main methodological aim of social psychiatrists, to combine methods of individual clinical analysis with sociological research and generalization.