The Battle of Dien Bien Phu (French: Bataille de Din Bin Phu pronounced [bataj d dj bj fy]; Vietnamese: Chin dch in Bin Ph, IPA: [tjn zk n n f]) was a climactic confrontation of the First Indochina War that took place between 13 March and 7 May 1954. It was fought between the French Union's colonial Far East Expeditionary Corps and Viet Minh communist revolutionaries. The United States was officially not a party to the war, but it was secretly involved by providing financial and material aid to the French Union, which included CIA contracted American personnel participating in the battle. The People's Republic of China and the Soviet Union similarly provided vital support to the Viet Minh, including most of their artillery and ammunition.

The French began an operation to insert, then support, their soldiers at in Bin Ph, deep in the autonomous Tai Federation up in the hills northwest of Tonkin. The operation's purpose was to cut off Viet Minh supply lines into the neighboring Kingdom of Laos (a French ally), and draw the Viet Minh into a major confrontation in order to cripple them. The plan was to resupply the French position by air, a strategy adopted based on the belief that the Viet Minh had no anti-aircraft capability. The Viet Minh, however, under General V Nguyn Gip, surrounded and besieged the French. They brought in vast amounts of heavy artillery (including anti-aircraft guns) and managed to move these bulky weapons through difficult terrain up the rear slopes of the mountains. They then dug tunnels through the mountains and arranged the guns to target the French position.

In March, a massive artillery bombardment by the Viet Minh ensued. The strategic positioning of their artillery made it nearly impervious to French counter-battery fire. Tenacious fighting on the ground ensued, reminiscent of the trench warfare of World War I. At times, the French repulsed Viet Minh assaults on their positions while supplies and reinforcements were delivered by air. As key positions were overrun, the perimeter contracted, and the air resupply on which the French had placed their hopes became impossible. As the Viet Minh anti-aircraft fire took its toll and artillery bombarded the airstrip effectively preventing takeoffs and landings, fewer and fewer of those supplies reached the French. The garrison was overrun in May after a two-month siege, and most of the French forces surrendered. A few of them escaped to Laos. The French government in Paris then resigned, and the new Prime Minister, the left-of-centre Pierre Mends France, supported French withdrawal from Indochina.

Of the 11,000 French troops captured, only 3,300 survived imprisonment.

The Battle of in Bin Ph was decisive; the war ended shortly afterward and the 1954 Geneva Accords were signed. France agreed to withdraw its forces from all its colonies in French Indochina, while stipulating that Vietnam would be temporarily divided at the 17th parallel, with control of the north given to the Viet Minh as the Democratic Republic of Vietnam under Ho Chi Minh, and the south becoming the State of Vietnam, nominally under Emperor Bo i, preventing Ho Chi Minh from gaining control of the entire country.

The First Indochina War (generally known as the Indochina War in France, and as the Anti-French Resistance War in Vietnam) began in French Indochina on December 19, 1946, and lasted until July 20, 1954. Fighting between French forces and their Việt Minh opponents in the south dated from September 1945. The conflict pitted a range of forces, including the French Union's French Far East Expeditionary Corps, led by the government of France and supported by the former emperor Bảo Đại's Vietnamese National Army against the People's Army of Vietnam and Việt Minh (part of the Communist Party), led by Võ Nguyên Giáp and Hồ Chí Minh. Most of the fighting took place in Tonkin in northern Vietnam, although the conflict engulfed the entire country and also extended into the neighboring French Indochina protectorates of Laos and Cambodia.

At the Potsdam Conference in July 1945, the Combined Chiefs of Staff decided that Indochina south of latitude 16° north was to be included in the Southeast Asia Command under British Admiral Mountbatten. The Japanese forces located south of that line surrendered to him and those to the north surrendered to Generalissimo Chiang Kai-shek. In September 1945, Chinese forces entered Tonkin, and a small British task force landed at city of Saigon (Cochinchina's capital). The Chinese accepted one Vietnamese government under Hồ Chí Minh, then in power in Hanoi (Tonkin's capital). The British refused to do likewise in Saigon, and deferred to the French there from the outset, against the ostensible support of the Việt Minh authorities by American OSS representatives. On V-J Day, September 2, Hồ Chí Minh had proclaimed in Hanoi the establishment of the Democratic Republic of Vietnam (DRV). The DRV ruled as the only civil government in all of Vietnam for a period of about 20 days, after the abdication of Emperor Bảo Đại, who had governed under the Japanese rule. On 23 September 1945, with the knowledge of the British commander in Saigon, French forces overthrew the local DRV government, and declared French authority restored in Cochinchina. Guerrilla warfare began around Saigon immediately, but the French gradually retook control of the South and North of Indochina. Hồ Chí Minh agreed to negotiate the future status of Vietnam, but the talks, held in France, failed to produce a solution. After over one year of latent conflict, all-out war broke out in December 1946 between French and Việt Minh forces as Hồ Chí Minh and his government went underground. The French tried to stabilize Indochina by reorganizing it as a Federation of Associated States. In 1949, they put former Emperor Bảo Đại back in power, as the ruler of a newly established State of Vietnam.

The first few years of the war involved a low-level rural insurgency against the French. In 1949 the conflict turned into a conventional war between two armies equipped with modern weapons supplied by the United States, China and the Soviet Union. French Union forces included colonial troops from their former empire - Moroccan, Algerian, and Tunisian Arabs/Berbers; Laotian, Cambodian and Vietnamese ethnic minorities; Black Africans - and French professional troops, European volunteers, and units of the Foreign Legion. The use of metropolitan recruits was forbidden by the government to prevent the war from becoming even more unpopular at home. It was called the "dirty war" (la sale guerre) by leftists in France.The strategy of pushing the Việt Minh into attacking well-defended bases in remote parts of the country at the end of their logistical trails was validated at the Battle of Nà Sản even though the base was relatively weak because of a lack of concrete and steel. French efforts were made more difficult due to the limited usefulness of armored tanks in a jungle environment, lack of strong air forces for air cover and carpet bombing, and use of foreign recruits from other French colonies (mainly from Algeria, Morocco and even Vietnam). Võ Nguyên Giáp, however, used efficient and novel tactics of direct fire artillery, convoy ambushes and massed anti-aircraft guns to impede land and air supply deliveries together with a strategy based on recruiting a sizable regular army facilitated by wide popular support, a guerrilla warfare doctrine and instruction developed in China, and the use of simple and reliable war material provided by the Soviet Union. This combination proved fatal for the bases' defenses, culminating in a decisive French defeat at the Battle of Dien Bien Phu.At the International Geneva Conference on July 21, 1954, the new socialist French government and the Việt Minh made an agreement which effectively gave the Việt Minh control of North Vietnam above the 17th parallel. The south continued under Bảo Đại. The agreement was denounced by the State of Vietnam and by the United States. A year later, Bảo Đại would be deposed by his prime minister, Ngô Đình Diệm, creating the Republic of Vietnam (South Vietnam). Soon an insurgency, backed by the north, developed against Diệm's government. The conflict gradually escalated into the Vietnam War (1955–1975).