The Falklands War (Spanish: Guerra de las Malvinas) was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British dependent territories in the South Atlantic: the Falkland Islands and its territorial dependency, South Georgia and the South Sandwich Islands. The conflict began on 2 April 1982, when Argentina invaded and occupied the Falkland Islands, followed by the invasion of South Georgia the next day. On 5 April, the British government dispatched a naval task force to engage the Argentine Navy and Air Force before making an amphibious assault on the islands. The conflict lasted 74 days and ended with an Argentine surrender on 14 June, returning the islands to British control. In total, 649 Argentine military personnel, 255 British military personnel, and three Falkland Islanders were killed during the hostilities.

The conflict was a major episode in the protracted dispute over the territories' sovereignty. Argentina claimed (and maintains) that the islands are Argentine territory, and the Argentine government thus described its military action as the reclamation of its own territory. The British government regarded the action as an invasion of a territory that had been a Crown colony since 1841. Falkland Islanders, who have inhabited the islands since the early 19th century, are predominantly descendants of British settlers, and strongly favour British sovereignty. Neither state officially declared war, although both governments declared the islands a war zone.

The conflict had a strong effect in both countries and has been the subject of various books, articles, films, and songs. Patriotic sentiment ran high in Argentina, but the unfavourable outcome prompted large protests against the ruling military government, hastening its downfall and the democratisation of the country. In the United Kingdom, the Conservative government, bolstered by the successful outcome, was re-elected with an increased majority the following year. The cultural and political effect of the conflict has been less in the UK than in Argentina, where it has remained a common topic for discussion.

Diplomatic relations between the United Kingdom and Argentina were restored in 1989 following a meeting in Madrid, at which the two governments issued a joint statement. No change in either country's position regarding the sovereignty of the Falkland Islands was made explicit. In 1994, Argentina adopted a new constitution, which declared the Falkland Islands as part of one of its provinces by law. However, the islands continue to operate as a self-governing British Overseas Territory.

In 1965, the United Nations called upon Argentina and the United Kingdom to reach a settlement of the sovereignty dispute. The UK Foreign and Commonwealth Office (FCO) regarded the islands as a nuisance and barrier to UK trade in South America. Therefore, while confident of British sovereignty, the FCO was prepared to cede the islands to Argentina. When news of a proposed transfer broke in 1968, elements sympathetic with the plight of the islanders were able to organise an effective parliamentary lobby to frustrate the FCO plans. Negotiations continued, but in general failed to make meaningful progress; the islanders steadfastly refused to consider Argentine sovereignty on one side, whilst Argentina would not compromise over sovereignty on the other. The FCO then sought to make the islands dependent on Argentina, hoping this would make the islanders more amenable to Argentine sovereignty. A Communications Agreement signed in 1971 created an airlink and later YPF, the Argentine oil company, was given a monopoly in the islands.

In 1977, the British prime minister, James Callaghan, in response to heightened tensions in the region and the Argentine occupation of Southern Thule, secretly sent a force of two frigates and a nuclear-powered submarine, HMS Dreadnought, to the South Atlantic, codenamed Operation Journeyman. It is unclear whether the Argentines were aware of their presence, but British sources state that they were advised of it through informal channels. Nevertheless, talks with Argentina on Falklands sovereignty and economic cooperation opened in December of that year, though they proved inconclusive.

In 1980, a new UK Minister of State for Foreign Affairs, Nicholas Ridley, went to the Falklands trying to sell the islanders the benefits of a leaseback scheme, which met with strong opposition from the islanders. On his return to London in December 1980, he reported to parliament but was viciously attacked over what was seen as a sellout. (It was unlikely that leaseback idea would have progressed further anyway since the British had sought a long-term lease of 99 years, whereas Argentina was pressing for a much shorter period of only thirty years.) At a private committee meeting that evening, it was reported that Ridley said: "If we don't do something, they will invade. And there is nothing we could do."

In the period leading up to the war—and, in particular following the transfer of power between the military dictators General Jorge Rafael Videla and General Roberto Eduardo Viola late in March 1981—Argentina had been in the midst of devastating economic stagnation and large-scale civil unrest against the National Reorganisation Process, the military junta that had been governing the country since 1976.