The Buddhist Uprising of 1966 (Vietnamese: Nổi dậy Phật giáo 1966), or more widely known in Vietnam as the Crisis in Central Vietnam (Biến động Miền Trung), was a period of civil and military unrest in South Vietnam, mostly in the I Corps area in the north of the country in central Vietnam. The area is a center of Vietnamese Buddhism, and at the time, activist Buddhist monks and civilians were at the forefront of opposition to a series of military juntas that had been ruling the nation, as well as prominently questioning the escalation of the Vietnam War.

During the rule of the Catholic Ngô Đình Diệm, the perceived discrimination against the Buddhist population generated the growth of Buddhist institutions as they sought to participate in national politics and gain better treatment. In 1965, after a series of military coups that followed the fall of the Diệm regime in 1963, Air Marshal Nguyễn Cao Kỳ and General Nguyễn Văn Thiệu finally established a stable junta, holding the positions of Prime Minister and figurehead Chief of State respectively. The Kỳ-Thiệu regime was initially almost a feudal system, being more of an alliance of warlords than a state as each corps commander ruled his area as his own fiefdom, handing some of the taxes they collected over to the government in Saigon and keeping the rest for themselves. During that time, suspicion and tension continued between the Buddhist and Catholic factions in Vietnamese society.

The religious factor combined with a power struggle between Kỳ and General Nguyễn Chánh Thi, the commander of I Corps, a Buddhist local to the region and popular in the area. Thi was a strong-willed officer regarded as a capable commander, and Kỳ saw him as a threat, as did others within the junta. In February 1966, Kỳ attended a summit in Honolulu, where he became convinced that he now had American support to move against Thi, the strongest and most able of the corps commanders. In March 1966, Kỳ fired Thi and ordered him into exile in the United States under the false pretense of medical treatment. This prompted both civilians and some I Corps units to launch widespread civil protests against Kỳ's regime and halt military operations against Viet Cong. Kỳ gambled by allowing Thi to return to I Corps before departing for the US, but the arrival of the general to his native area only fuelled anti-Kỳ sentiment. The Buddhist activists, students and Thi loyalists in the military coalesced into the "Struggle Movement", calling for a return to civilian rule and elections. Meanwhile, Thi stayed in I Corps and did not leave; strikes and protests stopped civilian activity in the area, government radio stations were taken over and used for anti-Kỳ campaigning, and military operations ceased. Riots also spread to the capital Saigon and other cities further south.

At the start of April, Kỳ decided to move. He declared that Da Nang, the main centre in I Corps, was under communist control and publicly vowed to kill the mayor, who had expressed support for the Struggle Movement. Kỳ moved military forces into the city and travelled there to prepare for an assault, but had to withdraw and then start discussions with Buddhist leaders, as it was obvious that he was not strong enough to crush the opposition. In the meantime, he fired Thi's successor Nguyễn Văn Chuân because he wanted a firmer attempt to regain control, and appointed Tôn Thất Đính to replace him. Đính claimed to have calmed the situation, but Kỳ viewed the situation as appeasement, and on May 15, his forces drove off Đính and took over. During the previous month, American forces had also become involved in the stand-off, and the Struggle Movement viewed their participation as biased towards Kỳ, leading to some tense confrontations.

In the second half of May, Kỳ's forces began to force the issue and gradually wore down the Struggle Movement as the rebel I Corps forces were worn down, despite some American objections that his aggressive attacks had the potential to cause too much collateral damage. At one stage, Kỳ's forces ended up in a skirmish with American forces, and later, the Americans were in the middle of a stand-off between the Vietnamese factions regarding a mined bridge. As Kỳ's forces took back Da Nang and Huế in street fighting, Struggle Movement supporters saw American intervention as being pro-Kỳ, and anti-US riots resulted in some American buildings being burnt down. Kỳ's triumph ended the Buddhist movement's influence on politics and he confined their leader Thích Trí Quang to house arrest thereafter, while Thi left for the United States.

South Vietnam was often portrayed as having a Buddhist majority, comprising 70% or more of the population. These figures, reported by foreign journalists, were overestimated, as Westerners commonly mistook folk religion for Buddhism. The actual number of Buddhists was much smaller, at most about 27%. Ngo Dinh Diem was regarded by "orthodox" historians as having pursued pro-Catholic policies that antagonized many Buddhists. The government was regarded as being biased towards Catholics in public service and military promotions, as well as the allocation of land and business favors.

The "private" status that was imposed on Buddhism by the French, which required official permission to conduct public Buddhist activities, was not repealed by Diệm. The white and gold Catholic flag was allegedly flown at major public events in South Vietnam. However, portrayals by Western media at the time were severely distorted, as Vietnamese Buddhism in fact flourished under Diệm's First Republic.

On May 8, 1963, Diệm's officials invoked a rarely enforced law to prohibit the display of religious flags, forbidding Buddhists from flying their flag on Vesak, the birthday of Gautama Buddha. This caused Buddhist indignation, as Catholic flags had been flown a week earlier at a celebration for Diệm's brother, Archbishop Ngô Đình Thục. On May 8, in Huế, a crowd of Buddhists protested against the ban on the Buddhist flag. The police and army opened fire and threw grenades at the demonstrators, leaving nine dead.