Phase III of the Tet Offensive of 1968 (also known as the August offensive or Third offensive) was launched by the People's Army of Vietnam (PAVN) and Viet Cong (VC) from 17 August to 27 September 1968. The offensive was divided into two waves of attacks from 17 to 31 August 1968 and from 11 to 27 September of that same year.

In late June 1968, COSVN and the commanders of Military Region 5 held a series of conferences to review the results of the May offensive, also in attendance was Lê Duẩn who had pushed for the original plan for the General Offensive–General Uprising. The majority of the attendees, including Chinese military advisers, regarded the May offensive as a failure and opposed any renewal of the offensive. Lê Duẩn supported by General Hoàng Văn Thái and General Chu Huy Mân then persuaded the attendees to support the launching of a third offensive by mid-August. The Chinese advisers opposed this decision and returned to China, while several of the Vietnamese who had voiced their opposition to the new offensive were fired. The offensives of May and August were primarily re-directed towards military targets, intending to blunt the perception that military victory was attainable for the United States (US).

On 24 July in Hanoi, Lê Duẩn met with senior leaders responsible for military affairs including PAVN chief of staff, General Văn Tiến Dũng to develop the operational plan for the offensive.

After considering the recommendations submitted by COSVN and Military Region 5, it was agreed that Tây Ninh Province with its proximity to base areas in Cambodia would be the main area of operations. Saigon would not be targeted because of the severe losses suffered by VC forces there in the Tet and May offensives and subsequent Allied security operations. The plan called for the 5th and 9th Divisions to draw the US 25th Infantry Division away from its positions between Tây Ninh and Dầu Tiếng allowing VC local force units to attack Tây Ninh. The 7th Division would attack Lộc Ninh in Bình Long Province to divert the US 1st Infantry Division and the Army of the Republic of Vietnam (ARVN) 5th Division from reinforcing Tây Ninh. Other PAVN/VC units would launch further diversionary attacks across the region.

In the Central Highlands the PAVN 1st Division was to seize the Duc Lap Camp and then move northeast to threaten Buôn Ma Thuột. The PAVN 24th Regiment would cut Highway 14 between Buôn Ma Thuột and Pleiku. The 95C and 101D Regiments would make diversionary attacks on Allied bases across Kon Tum Province, while in the lowland areas VC units would make attacks by fire and sapper attacks on Allied bases.

In central I Corps the PAVN 31st and 38th Regiments would attack the 1st Marine Division positions around Đà Nẵng allowing 6 VC local force battalions to penetrate and attack key installations across the city while the PAVN 368B Artillery Regiment would shell Da Nang Air Base.

In southern I Corps a reinforced regiment from the PAVN 2nd Division would attack Tam Kỳ and another reinforced regiment from the PAVN 3rd Division would attack Quảng Ngãi.

Allied intelligence was able to detect the planning of the offensive, its timing and objectives. On 10 August COMUSMACV General Creighton Abrams reported to the US Joint Chiefs of Staff that the “current deployment of [allied] ground forces is satisfactory,” and he was “confident in our ability” to defeat the offensive. Abrams ordered increased air strikes on suspected PAVN/VC assembly areas, but specifically ordered his commanders not to be drawn out into the countryside, but rather to stay back and defend the population centers.