The National Front for the Liberation of Vietnam (Vietnamese Mặt Trận Giải Phóng Miền Nam Việt Nam) or National Liberation Front was known to American and allied soldiers in Vietnam as the Viet Cong—from a contraction for the Vietnamese phrase Việt Nam Cộng Sản, or "Vietnamese Communist."
This derogatory phrase was used by the Republic of Vietnam (RVN) government of South Vietnam under President Ngo Dinh Diem to describe his political opponents, many of whom were Communists, starting after the 1954 partition of Vietnam between the RVN in the south and the Democratic Republic of Vietnam (DRV) in the north. Later, during the Vietnam War, the RVN and the United States government used this expression to refer to the National Front for the Liberation of Vietnam (NLF) and its guerrilla army, the People's Liberation Armed Forces (PLAF). (The NLF and the PLAF never used this expression to refer to themselves, and always asserted that they were a national front of all anti-RVN forces, communist or not.) It is this use of "Viet Cong" that most people in the United States and Europe are most familiar with.
In 1969, the National Front formed a provisional Republic of South Vietnam which took power briefly after the fall of Saigon in 1975 and before the reunification of the country under the leadership of the Communist Party of Vietnam as the Socialist Republic of Vietnam in 1976.