The National Front for the Liberation of Southern Vietnam (Vietnamese Mặt Trận Giải Phóng Miền Nam Việt Nam), also known as the National Liberation Front (NLF) and as Front National de Liberté (FNL), was the primary rebel organization fighting the Colonialist French regime under Diem Bien Phu and later the US-backed Republic of Vietnam during the Vietnam War. The NLF asserted that it was a national front of all elements opposed to the existing government, whether communist or not. Its military organization was known as the People's Liberation Armed Forces.

American soldiers and the South Vietnam government typically referred to their guerrilla opponents as the "Viet Cong".

In 1969, the NLF 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.

The U.S. military complained that the NLF often diguised themselves as civilians, and thus U.S. troops could not tell the difference between the NLF and civilians. During the Vietnam War, U.S. policy was to treat captured NLF and North Vietnamese regulars as Enemy Prisoners of War under the Geneva Convention of 1949.