The Viet Cong (can be abbreviated as VC, sometimes spelled as Vietcong), officially the National Liberation Front of South Vietnam, was an armed communist organization in South Vietnam, Laos and Cambodia. It fought under the direction of North Vietnam against the South Vietnamese and United States governments during the Vietnam War. It had both guerrilla and regular army units, as well as a network of cadres who organized and mobilized peasants in the territory the Viet Cong controlled. During the war, communist fighters and anti-war activists claimed that the Viet Cong was an insurgency indigenous to the South, while the U.S. and South Vietnamese governments portrayed the group as a tool of North Vietnam. According to Trần Văn Trà, the Viet Cong's top commander, and the post-war Vietnamese government's official history, the Viet Cong followed orders from Hanoi and were part of the People's Army of Vietnam, or North Vietnamese army.

North Vietnam established the Viet Cong on December 20, 1960, at Tân Lập village in Tây Ninh Province to foment insurgency in the South. Many of the Viet Cong's core members were volunteer "regroupees", southern Viet Minh who had resettled in the North after the Geneva Accord (1954). Hanoi gave the regroupees military training and sent them back to the South along the Ho Chi Minh trail in the late 1950s and early 1960s. The Viet Cong called for the unification of Vietnam and the overthrow of the American backed South Vietnamese government. The Viet Cong's best-known action was the Tet Offensive, an assault on more than 100 South Vietnamese urban centers in 1968, including an attack on the U.S. embassy in Saigon. The offensive riveted the attention of the world's media for weeks, but also overextended the Viet Cong. Later communist offensives were conducted predominantly by the North Vietnamese. The organization officially merged with the Fatherland Front of Vietnam on February 4, 1977, after North and South Vietnam were officially unified under a communist government.