The Mỹ Lai Massacre was the mass murder of unarmed South Vietnamese civilians by U.S. troops in Sơn Tịnh District, South Vietnam, on March 16, 1968 during the Vietnam War.
Between 347 and 504 unarmed people were killed by U.S. Army soldiers, victims including men, women, children, and infants. Twenty-six soldiers were charged with criminal offenses, but only Lieutenant William Calley Jr., a platoon leader, was convicted. Found guilty of killing 22 villagers, he was originally given a life sentence, but served only three-and-a-half years under house arrest.

This war crime was later called "the most shocking episode of the Vietnam War".