The Killing Fields (Khmer: វាលពិឃាត, Khmer pronunciation: [ʋiəl pikʰiət]) are sites in Cambodia where collectively more than 1.3 million people were killed and buried by the Communist Party of Kampuchea during Khmer Rouge rule from 1975 to 1979, immediately after the end of the Cambodian Civil War (1970–75). The mass killings were part of the broad, state-sponsored Cambodian genocide. The Cambodian journalist Dith Pran coined the term "killing fields" after his escape from the regime.

The Khmer Rouge regime arrested and eventually executed almost everyone suspected of connections with the former government or foreign governments, as well as professionals and intellectuals. Ethnic Vietnamese, Thai, Chinese, Cham along side Cambodian Christians, and Buddhist monks were the demographic targets of persecution. As a result, Pol Pot has been described as "a genocidal tyrant". Sociologist Martin Shaw described the Cambodian genocide as "the purest genocide of the Cold War era". In 1979, Vietnam invaded Democratic Kampuchea and toppled the Khmer Rouge regime, ending the genocide.

After five years of researching 20,000 grave sites, analysis indicates at least 1,386,734 victims of execution. Estimates of total deaths resulting from Khmer Rouge policies, including from disease and starvation, range from 1.7 to 2.2 million, out of a 1975 population of roughly 8 million. Even the Khmer Rouge acknowledged 2 million had been killed—though they attributed those deaths to the subsequent Vietnamese invasion.

By late 1979, UN and Red Cross officials were warning that another 2.2 million Cambodians faced death by starvation due to "the near destruction of Cambodian society under the regime of ousted Prime Minister Pol Pot", who were saved by international aid after the Vietnamese invasion.

The judicial process of the Khmer Rouge regime, for minor or political crimes, began with a warning from the Angkar, the government of Cambodia under the regime. People receiving more than two warnings were sent for "re-education", which meant near-certain death. People were often encouraged to confess to Angkar their "pre-revolutionary lifestyles and crimes" (which usually included some kind of free-market activity; having had contact with a foreign source, such as a U.S. missionary, international relief or government agency; or contact with any foreigner or with the outside world at all), being told that Angkar would forgive them and "wipe the slate clean." They were then taken away to a place such as Tuol Sleng or Choeung Ek for torture or execution.^{[citation needed]}

The executed were buried in mass graves. In order to save ammunition, the executions were often carried out using poison or improvised weapons such as sharpened bamboo sticks, hammers, machetes and axes. Inside the Buddhist Memorial Stupa at Choeung Ek, there is evidence of bayonets, knives, wooden clubs, hoes for farming and curved scythes being used to kill victims, with images of skulls, damaged by these implements, as evidence. In some cases the children and infants of adult victims were killed by having their heads bashed against the trunks of Chankiri trees, and then were thrown into the pits alongside their parents. The rationale was "to stop them growing up and taking revenge for their parents' deaths."

In 1997 the Cambodian government asked for the UN's assistance in setting up a genocide tribunal. It took nine years to agree to the shape and structure of the court—a hybrid of Cambodian and international laws—before the judges were sworn in, in 2006. The investigating judges were presented with the names of five possible suspects by the prosecution on 18 July 2007. On 19 September 2007 Nuon Chea, second in command of the Khmer Rouge and its most senior surviving member, was charged with war crimes and crimes against humanity. He faced Cambodian and foreign judges at the special genocide tribunal and was convicted on 7 August 2014 and received a life sentence. On 26 July 2010 Kang Kek Iew (aka Comrade Duch), director of the S-21 prison camp, was convicted of crimes against humanity and sentenced to 35 years' imprisonment. His sentence was reduced to 19 years, as he had already spent 11 years in prison. On 2 February 2012, his sentence was extended to life imprisonment by the Extraordinary Chambers in the Courts of Cambodia. He died on 2 September 2020.

After five years of researching 20,000 grave sites, analysis indicates at least 1,386,734 victims of execution.