William Laws Calley Jr. is a former United States Army officer and war criminal who was convicted by court-martial for the murder of 22 unarmed South Vietnamese civilians in the My Lai massacre on March 16, 1968, during the Vietnam War. Calley was released to house arrest under orders by President Richard Nixon three days after his conviction. A new trial was ordered by the United States Court of Appeals for the Fifth Circuit but that ruling was overturned by the Supreme Court. Calley served three years of house arrest for the murders. Public opinion at the time about Calley was divided. Since his dismissal from the U.S. Army and release from prison, Calley has avoided public attention.

The My Lai massacre was a war crime committed by United States Army personnel on 16 March 1968, involving the mass murder of unarmed civilians in Sơn Tịnh district, South Vietnam, during the Vietnam War. Between 347 and 504 civilians were killed by U.S. soldiers from Company C, 1st Battalion, 20th Infantry Regiment and Company B, 4th Battalion, 3rd Infantry Regiment, 11th Brigade, 23rd (Americal) Infantry Division. Victims included men, women, children, and infants. Some of the women were gang-raped and their bodies mutilated, and some soldiers mutilated and raped children who were as young as 12. It is the largest publicized massacre of civilians by U.S. forces in the 20th century.