The Mapuche ( (Mapuche & Spanish: [mapute])) are a group of indigenous inhabitants of present-day south-central Chile and southwestern Argentina, including parts of present-day Patagonia. The collective term refers to a wide-ranging ethnicity composed of various groups who shared a common social, religious, and economic structure, as well as a common linguistic heritage as Mapudungun speakers. Their influence once extended from Aconcagua Valley to Chilo Archipelago and later spread eastward to Puelmapu, a land comprising part of the Argentine pampa and Patagonia. Today the collective group makes up over 80% of the indigenous peoples in Chile, and about 9% of the total Chilean population. The Mapuche are particularly concentrated in the Araucana region. Many have migrated from rural areas to the cities of Santiago and Buenos Aires for economic opportunities.

The Mapuche traditional economy is based on agriculture; their traditional social organization consists of extended families, under the direction of a lonko or chief. In times of war, the Mapuche would unite in larger groupings and elect a toki (meaning "axe" or "axe-bearer") to lead them. Mapuche material culture is known for its textiles and silverwork.

At the time of Spanish arrival, the Araucanian Mapuche inhabited the valleys between the Itata and Toltn rivers. South of there, the Huilliche and the Cunco lived as far south as the Chilo Archipelago. In the seventeenth, eighteenth and nineteenth centuries, Mapuche groups migrated eastward into the Andes and pampas, fusing and establishing relationships with the Poya and Pehuenche. At about the same time, ethnic groups of the pampa regions, the Puelche, Ranquel and northern Aonikenk, made contact with Mapuche groups. The Tehuelche adopted the Mapuche language and some of their culture, in what came to be called Araucanization, during which Patagonia came under effective Mapuche suzerainty.

Mapuche in the Spanish-ruled areas, especially the Picunche, mingled with Spanish during the colonial period, forming a mestizo population that lost its indigenous identity. But Mapuche society in Araucana and Patagonia remained independent until the late nineteenth century, when Chile occupied Araucana and Argentina conquered Puelmapu. Since then the Mapuche have become subjects, and then nationals and citizens of the respective states. Today, many Mapuche and Mapuche communities are engaged in the so-called Mapuche conflict over land and indigenous rights in both Argentina and in Chile.

The Battle of Tucapel (also known as the Disaster of Tucapel) is the name given to a battle fought between Spanish conquistador forces led by Pedro de Valdivia and Mapuche (Araucanian) Indians under Lautaro that took place at Tucapel, Chile on December 25, 1553. This battle happened in the context of the first stage of the Arauco War, named the "offensive war" within a larger uprising by Araucanians against the Spanish conquest of Chile. It was a defeat for the Spaniards, resulting in the capture and eventual death of Valdivia.