Action T4 (German: Aktion T4) was a program in Nazi Germany between 1939 and 1941, during which the regime of Adolf Hitler systematically killed between 75,000 to 100,000 people with intellectual or physical disabilities. The codename T4 was an abbreviation of “Tiergartenstrasse 4”, the address of a villa in the Berlin borough of Tiergarten which was the headquarters of the General Foundation for Welfare and Institutional Care (Gemeinnnützige Stiftung für Heil und Anstaltspflege). This body operated under the direction of Philipp Bouhler, the head of Hitler’s private chancellery, and Dr Karl Brandt, Hitler’s personal physician. This villa no longer exists, but a plaque set in the pavement on Tiergartenstrasse marks its location.
The T4 program developed from the Nazi Party’s policy of “racial hygiene,” the belief that the German people needed to be “cleansed” of “racially unsound” elements, which included people with disabilities. The program set important precedents for the later Holocaust of the Jews of Europe: the historian Ian Kershaw has called it “a vital step in the descent into modern barbarism.”