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 as 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.

Following the 1965 30 September Movement, Indonesian president Sukarno was overthrown by General Suharto. A key event in the transition to the New Order was the killing of over a million alleged communists between 1965 and 1966, including Sukarno's supporters, members of the Communist Party of Indonesia, labor and farming unions, intellectuals, and Chinese Indonesians. Backed by Western governments, the paramilitary groups and preman gangsters responsible for the massacres, the biggest being the Pancasila Youth, gained power in Indonesia.

The Act of Killing is directed by Joshua Oppenheimer, who with his crew in Medan, asks some of the gangsters to re-enact their killings. The film's first subjects, Anwar Congo and Herman Koto, used to sell black market tickets outside of a cinema. During the rise of communism, American films were restricted, and with no income they began working for a death squad as part of the genocide. Inspired by film noir films, killing methods include strangulation, stabbing, and throwing people into rivers. Congo estimates that he has killed as many as 1,000 people. The Pancasila Youth openly brag about their role in the massacres on television and express their intention to further curb the spread of "neocommunism" and far-leftism in Indonesia, and is backed by high-ranking government members, including then-vice president Jusuf Kalla. The ethnic Chinese who were not killed continue to have their money extorted by the gangsters.

Adi Zulkadry, a friend and past collaborator of Congo and participant in the genocide, discusses Pengkhianatan G30S/PKI (1984), a propaganda film that pushes the notion the 30 September Movement was perpetrated by the communists, and glorifies the genocide. While Congo praises the film for validating his acts, Zulkadry is sceptical of its plot and deems the genocide cruel. In a discussion with Oppenheimer, he denies it being a war crime, as the same holds true for the Iraq War and the Native American genocide in the United States. Congo then details his nightmares following the genocide, where he would envision the spirits of his victims. Zulkadry, who felt no remorse, downplays it as nerve issues. Ibrahim Sinik and Soduaon Siregar, journalists of Medan Pos who covered the genocide, show support but deny direct participation.

Koto runs in the 2009 Indonesian legislative election as a candidate from the Workers and Employers Party intending to extort locals once in office, but is easily defeated. Many high-ranking government officials are also leaders of Pancasila Youth factions, allowing them to commit corruption, rig elections, and clear land for developers. The group earns income in the modern era through criminal activities like gambling and drug smuggling. The film also depicts their sexual objectification of women; members boast about raping teenage girls and Gerwani members during the massacres.