The I Corps Tactical Zone was a corps of the Army of the Republic of Vietnam (ARVN), the army of the nation state of South Vietnam that existed from 1955 to 1975. It was one of four corps which the ARVN oversaw. This was the northernmost region of South Vietnam, bordering North Vietnam. These five provinces are Quảng Trị Province, (Khe Sanh, Đông Hà, Quang Tri City), Thừa Thiên-Huế Province, (Phu Bai, Hue City), Quảng Nam Province, (Đà Nẵng, Hoi An), Quang Tin Province, (Tam Ky, Chu Lai) and Quang Ngai Province, (Quang Ngai).
Among its formations and units were the 1st Division.
The I CTZ, later Military Region 1, was partnered with the U.S. III Marine Expeditionary Force and the XXIV Corps.
Map depicting the military regions of South Vietnam including the I Corps/1Ctz area.
See also 
- Tucker, Spencer C. (2000). Encyclopedia of the Vietnam War. Santa Barbara, California: ABC-CLIO. pp. 526–533. ISBN 1-57607-040-9.