A death squad is an armed group whose primary activity is carrying out extrajudicial killings, massacres, or enforced disappearances as part of political repression, genocide, ethnic cleansing, or revolutionary terror. Except in rare cases in which they are formed by an insurgency, domestic or foreign governments actively participate in, support, or ignore the death squad's activities.

Death squads are distinguished from assassination groups^{[example needed]} by their permanent organization and the larger number of victims (typically thousands or more) who may not be prominent individuals. Other violence, such as rape, torture, arson, or bombings may be carried out alongside murders. They may comprise a secret police force, paramilitary militia groups, government soldiers, policemen, or combinations thereof. They may also be organized as vigilantes, bounty hunters, mercenaries, or contract killers. When death squads are not controlled by the state, they may consist of insurgent forces or organized crime, such as the ones used by cartels.

Although the term "death squad" was not widely used until the activities of such groups became widely known in Central and South America during the 1970s and 80s, death squads have been employed under different guises throughout history. The term was first used by the fascist Iron Guard in Romania. It officially installed Iron Guard death squads in 1936 in order to kill political enemies. It was also used during the Battle of Algiers by Paul Aussaresses.

In Latin America, death squads first appeared in Brazil where a group called Esquadrão da Morte (literally "Death Squad") emerged in the 1960s; they subsequently spread to Argentina and Chile in the 1970s, and they were later used in Central America during the 1980s. Argentina used extrajudicial killings as a way of crushing the liberal and communist opposition to the military junta during the "Dirty War" of the 1970s. For example, Alianza Anticomunista Argentina was a far-right death squad mainly active during the "Dirty War". The Chilean military regime of 1973–1990 also committed such killings. See Operation Condor for examples.

During the Salvadoran Civil War, death squads became notorious following the assassination of Archbishop Óscar Romero by a sniper as he said Mass inside a convent chapel on 24 March 1980. In December 1980, three American nuns, Ita Ford, Dorothy Kazel, and Maura Clarke, and a lay worker, Jean Donovan, were gang raped and murdered by a military unit later found to have been carrying out orders. Death squads were instrumental in killing hundreds of real and suspected Communists. Priests who were spreading liberation theology, such as Father Rutilio Grande, were also targeted. The murderers in this case were found to have been soldiers from the Salvadoran military, which was receiving U.S. funding and had U.S. military advisors during the Carter administration. These events prompted outrage in the U.S. and led to a temporary ending of military aid at the end of his presidency.

Honduras also had death squads active through the 1980s, the most notorious of which was the army unit Battalion 316. Hundreds of people, teachers, politicians, and union leaders were assassinated by government-backed forces. Battalion 316 received substantial training from the United States Central Intelligence Agency.

In Southeast Asia, extrajudicial killings were conducted by both sides during the Vietnam War.

As of 2010^[update], death squads have continued to be active in Chechnya.