The Khmer Republic or République Khmère, was the republican government of Cambodia that was formally declared on October 9, 1970. The Khmer Republic was disestablished in 1975 and was followed by the totalitarian state known as Democratic Kampuchea.

Formally declared on October 9, 1970, the Khmer Republic was a right-wing pro-United States military-led government headed by General Lon Nol and Prince Sisowath Sirik Matak that took power in the March 18, 1970 coup against Prince Norodom Sihanouk, then the country's head of state.

The main causes of the coup were Norodom Sihanouk's toleration of North Vietnamese activity within Cambodia's borders, allowing heavily armed Vietnamese Communist outfits de facto control over vast areas of eastern Cambodia. Another important factor was the dire state of the Cambodian economy, an indirect result of Sihanouk's policies of pursuing neutrality through virulent anti-Americanism.^{[page needed]}

With the removal of Sihanouk, the existing Kingdom of Cambodia became a republic, although the throne had been officially vacant for some years since the death of King Norodom Suramarit. The character of the new regime was right-wing and nationalist; most significantly, it ended Sihanouk's period of covert cooperation with the North Vietnamese regime and the Viet Cong, and aligned Cambodia with South Vietnam in the ongoing Second Indochina War. The Khmer Republic was opposed within the Cambodian borders by the Front Uni National du Kampuchea or FUNK, a relatively broad alliance between Sihanouk, his supporters, and the Communist Party of Kampuchea. The insurgency itself was conducted by the CPNLAF, the Cambodian People's National Liberation Armed Forces: they were backed by both the People's Army of Vietnam (PAVN) and the National Liberation Front (NLF, better known as the Viet Cong), who occupied parts of Cambodia as part of their ongoing war with the South Vietnamese.