The Basque conflict, also known as the Spain–ETA conflict, was an armed and political conflict from 1959 to 2011 between Spain and the Basque National Liberation Movement, a group of social, terrorist and political Basque organizations which sought independence from Spain and France. The movement was built around the terrorist organization ETA, which had launched a campaign of attacks against Spanish administrations since 1959. ETA had been proscribed as a terrorist organization by the Spanish, British, French and American authorities at different moments. The conflict took place mostly on Spanish soil, although to a smaller degree it was also present in France, which was primarily used as a safe haven by ETA members. It was the longest running violent conflict in modern Western Europe. It has been sometimes referred to as "Europe's longest war".

ETA, an acronym for Euskadi Ta Askatasuna, was an armed Basque nationalist and far-left separatist organization in the Basque Country between 1959 and 2018, with its goal being independence for the region. The group was founded in 1959 during the era of Francoist Spain, and later evolved from a pacifist group promoting traditional Basque culture to a violent paramilitary group. It engaged in a campaign of bombings, assassinations, and kidnappings throughout Spain and especially the Southern Basque Country against the regime, which was highly centralised and hostile to the expression of non-Castilian minority identities. ETA was the main group within the Basque National Liberation Movement and was the most important Basque participant in the Basque conflict.