The My Lai Massacre was a United States war crime committed on 16 March 1968, involving the mass murder of unarmed civilians in Sơn Mỹ village, Quảng Ngãi province, South Vietnam, during the Vietnam War.

At least 347 and up to 504 civilians, almost all women, children and elderly men, were murdered by U.S. Army soldiers. Some of the women were gang-raped and their bodies mutilated, and some soldiers mutilated and raped children as young as 12.

The incident is the largest confirmed massacre of civilians by U.S. forces in the 20th century.