The Act of Killing (Indonesian: Jagal, lit. 'Butcher') is a 2012 documentary film directed by Joshua Oppenheimer, with Christine Cynn and an anonymous Indonesian co-directing. The film follows individuals who participated in the Indonesian mass killings of 1965–66, wherein alleged communists and people opposed to the New Order regime were tortured and killed, with the killers, many becoming gangsters, still in power throughout the country. The film was mostly filmed in Medan, North Sumatra, following the executioner Anwar Congo and his acquaintances as they, upon Oppenheimer's request, re-enact their killings and talk about their actions openly, also following Congo's psychological journey facing the topic.

A co-production between Denmark, Indonesia, Norway and the United Kingdom, it is presented by Final Cut for Real in Denmark and produced by Signe Byrge Sørensen, with Werner Herzog, Errol Morris, Joram ten Brink and Andre Singer in executive producer roles. The film was conceived following Oppenheimer and Cynn's Indonesian documentary film The Globalisation Tapes (2003), which depicted survivors of the killings, who ideated The Act of Killing. They interviewed 40 people who were unexpectedly boastful about their actions, before taking an interest on Congo in 2005 due to his humanist quality. Filming occurred up to 2011 with an Indonesian team largely credited anonymous. Oppenheimer described the process as taking a psychological toll on their mental health. The film was edited by a team of four.

The Act of Killing premiered on 31 August 2012 at the Telluride Film Festival in the United States, which was followed by more festival and theatrical screenings up to 2014. The initial releases used a 120-minute cut, with the 2013 television airings trimming it further up to 95 minutes. Due to its positive reception, the 160-minute director's cut, previously only shown in Indonesia, was released for international audiences. The Indonesian release began on 1 November 2012 secretly, but public releases were later seen, and popularity spiked in the country too. It was later released for free online only for people in Indonesia. The film received widespread acclaim from critics for its method in tackling the subject, blending surrealism with realism. It has entered lists of the best films by various critics, and has earned various accolades including a British Academy Film Award.

The film has become subject to scholarly analysis regarding documentary filmmaking, and the mass killings itself. It has also helped catalyse a wide conversation regarding the events in Indonesia, with the reality of what happened more known, especially with the Western world's direct involvement. In China, the film sparked outrage due to the depiction of the gangsters extorting money from Chinese Indonesians. The Indonesian government has not given positive responses, claiming that it is a misleading portrayal of the country's history. A spiritual successor, The Look of Silence, was released in 2014; it depicts the family of a victim as they encounter the killers and understand further on what happened.