COSVN, pronounced "CŎS-vĭn" and standing for Central Office for South Vietnam (Vietnamese: Văn phòng Trung ương Cục miền Nam), was the American term for People's Army of Vietnam (PAVN) political and military headquarters during the Vietnam War. It was envisaged as being in overall command of the communist effort in the southern half of the Republic of Vietnam (South Vietnam), which included the efforts of both PAVN and the Vietcong. Whether COSVN actually existed, and if so, where it was located at any one time, and how important it might have been, were contentious subjects, but in his memoirs the American commander in South Vietnam, General William C. Westmoreland spoke of it as something whose existence and importance were not in doubt. All U.S. and South Vietnamese efforts to eliminate it during the conflict failed.

The headquarters was reportedly created in 1961 when the southern and central branches of the Lao Dong Party (the Vietnamese Communist Party) merged into the Central Directorate for the South. An advance element of the Party's Central Committee, the headquarters was chartered to direct VC guerrilla operations in South Vietnam. Major General Tran Luong came south in May 1961 to reorganize the structure of the Directorate and its subordinate regions, Military Regions 1, 2, 3, 4, 6 and 10, known collectively as the B-2 Front. In the process, he created COSVN.