Gustav Aschaffenburg (May 23, 1866 – September 2, 1944) was a German psychiatrist born in Zweibrücken.
In 1890 he received his medical doctorate from the University of Strasbourg with a thesis on delirium tremens. Later he worked as an assistant to Emil Kraepelin at the psychiatric university clinic in Heidelberg. He then practiced psychiatric medicine at the University of Halle and at the Akademie für praktische Medizin in Cologne (from 1919 the University of Cologne).
In the 1930s Aschaffenburg's academic career at Cologne was terminated by the Nazi edict, Gesetz zur Wiederherstellung des Berufsbeamtentums, and he eventually emigrated to the United States, working as a professor at the Catholic University of America in Washington D.C. and at Johns Hopkins University in Baltimore.
Aschaffenburg was a pioneer in the fields of criminology and forensic psychiatry. In 1903 he published an early systematic study on the causes of crime titled "Das Verbrechen und seine Bekämpfung", in which he discusses individual-hereditary and social-environmental factors, and also dismisses Cesare Lombroso's idea of the so-called "born criminal". Later the work was translated into English, and published as Crime and Its Repression (1913).