The Arauco War was a conflict between colonial Spaniards and the Mapuche people in what is now the Araucanía and Biobío regions of modern Chile. The conflict lasted three centuries, with its conclusion in the late 19th century marking one of the final episodes in the European conquest of the Americas.

The beginning of the conflict is usually placed at the Battle of Reynogüelén, which occurred in 1536 between an expedition of Diego de Almagro and a well-organized and numerous group of Mapuche soldiers, near the confluence of the Ñuble and Itata rivers.

Its end, however, is more difficult to pin down. After 1609, each governor of Chile held Parlamentos with the Mapuche chiefs, in which they discussed peace with the Mapuche leaders. Finally the Mupuche under the Toqui Lincopinchon agreed to a peace treaty at the 1641 Parliament of Quillin. Later Parliaments would discuss the maintenance or restoration of a treaty between the parties, violations of which were quite frequent, occasionally escalating into large scale warfare. Spain ended its last hostilities with the Mapuche at the 1793 Parliament of Negrete and reinforced the peace in the 1803 Parliament of Negrete.