Operation Toan Thang I was a U.S. Army, Army of the Republic of Vietnam (ARVN), 1st Australian Task Force and Royal Thai Volunteer Regiment operation conducted between 8 April and 31 May 1968 in the Vietnam War. The operation was part of a reaction to the Tet Offensive designed to put pressure on Vietcong (VC) and People's Army of Vietnam (PAVN) forces in III Corps.

The Tet Offensive was a major escalation and one of the largest military campaigns of the Vietnam War. The Viet Cong (VC) and North Vietnamese People's Army of Vietnam (PAVN) launched a surprise attack on January 30, 1968 against the forces of the South Vietnamese Army of the Republic of Vietnam (ARVN), the United States Armed Forces and their allies. It was a campaign of surprise attacks against military and civilian command and control centers throughout South Vietnam. The name is the truncated version of the Lunar New Year festival name in Vietnamese, Tết Nguyên Đán, with the offense chosen during a holiday period as most ARVN personnel were on leave. The purpose of the wide-scale offensive by the Hanoi Politburo was to trigger political instability in a belief that mass armed assault on urban centers would trigger defections and rebellions.