The Killing Fields are a number of sites in Cambodia where collectively more than one million people were killed and buried by the Khmer Rouge regime (the Communist Party of Kampuchea) during its rule of the country from 1975 to 1979, immediately after the end of the Cambodian Civil War (1970–1975). The mass killings were part of a broad state-sponsored genocide (the Cambodian genocide).

Analysis of 20,000 mass grave sites by the DC-Cam Mapping Program and Yale University indicates at least 1,386,734 victims of execution. Estimates of the total deaths resulting from Khmer Rouge policies, including death from disease and starvation, range from 1.7 to 2.5 million out of a 1975 population of roughly 8 million. In 1979, Vietnam invaded Democratic Kampuchea and toppled the Khmer Rouge regime, ending the 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 with foreign governments, as well as professionals and intellectuals. Ethnic Vietnamese, ethnic Thai, ethnic Chinese, ethnic Cham, Cambodian Christians, and Buddhist monks were the demographic targets of persecution. As a result, Pol Pot has been described as "a genocidal tyrant". Martin Shaw described the Cambodian genocide as "the purest genocide of the Cold War era".
Ben Kiernan estimates that about 1.7 million people were killed. Researcher Craig Etcheson of the Documentation Center of Cambodia suggests that the death toll was between 2 and 2.5 million, with a "most likely" figure of 2.2 million. After five years of researching some 20,000 grave sites, he concludes that "these mass graves contain the remains of 1,386,734 victims of execution". A United Nations investigation reported 2–3 million dead, while UNICEF estimated 3 million had been killed.Demographic analysis by Patrick Heuveline suggests that between 1.17 and 3.42 million Cambodians were killed, while Marek Sliwinski suggests that 1.8 million is a conservative figure.Even the Khmer Rouge acknowledged that 2 million had been killed—though they attributed those deaths to a subsequent Vietnamese invasion. By late 1979, UN and Red Cross officials were warning that another 2.25 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.