The Cambodian genocide (Khmer: ហាយនភាពខ្មែរ or ការប្រល័យពូជសាសន៍ខ្មែរ, French: Génocide cambodgien) was carried out by Khmer Rouge under the leadership of Pol Pot, who radically pushed Cambodia towards communism. The movement resulted in the deaths of approximately 1.5 to 2 million people from 1975 to 1979, nearly a quarter of Cambodia's 1975 population (c. 7.8 million)

Pol Pot and Khmer Rouge had long been supported by the Communist Party of China (CPC) and Mao Zedong himself; it is estimated that at least 90% of the foreign aids to Khmer Rouge came from China, with 1975 alone seeing at least US$1 billion in interest-free economics and military aid and US$20 million gift from China. After seizing power in April 1975, the Khmer Rouge wanted to turn the country into a socialist agrarian republic, founded on the policies of ultra-Maoism and influenced by the Cultural Revolution. Pol Pot and other Khmer Rouge officials met with Mao Zedong in Beijing in June 1975, receiving approval and advice, while high-ranking CPC officials such as Zhang Chunqiao later visited Cambodia to offer help. In order to fulfill their goals, the Khmer Rouge emptied the cities and forced Cambodians to relocate to labor camps in the countryside, where mass executions, forced labor, physical abuse, malnutrition, and disease were prevalent. They also started the "Maha Lout Ploh", copying the "Great Leap Forward" of China which caused tens of millions of death in the Great Chinese Famine. In 1976, the Khmer Rouge changed the name of the country to Democratic Kampuchea.

By January 1979, approximately 2 million people died due to the policies of Khmer Rouge, including 200-300 thousand Chinese Cambodians, 90 thousand Muslims, and 20 thousand Vietnamese Cambodians. Some 20,000 people passed through the Security Prison 21, one of the 196 prisons operated by the Khmer Rouge, and only 7 adults survived. The prisoners were taken to the Killing Fields, where they were executed (often with pickaxes in order to save bullets) and buried in mass graves. The abduction and indoctrination of children was widespread, and many were persuaded or forced to commit atrocities. As of 2009, the Documentation Center of Cambodia has mapped some 23,745 mass graves containing approximately 1.3 million suspected victims of execution. Direct execution is believed to account for roughly 60% of the full death toll during the genocide, with other victims succumbing to starvation, exhaustion, or disease.

The genocide triggered a second outflow of refugees, many of whom escaped to neighboring Vietnam and, to a lesser extent, Thailand. The Vietnamese invasion of Cambodia ended the genocide by defeating the Khmer Rouge in January, 1979. On 2 January 2001, the Cambodian government established the Khmer Rouge Tribunal, to try the members of the Khmer Rouge leadership responsible for the Cambodian genocide. Trials began on 17 February 2009. On 7 August 2014, Nuon Chea and Khieu Samphan were convicted and received life sentences for crimes against humanity during the genocide