The Araucanization of Patagonia (Spanish: Araucanización de la Patagonia) was the process of expansion of Mapuche culture, influence and language from Araucanía into the Patagonic plains. Historians disagree in the time of the expansion but it would have occurred sometime between 1550 and 1850. Amerindian peoples such as the Puelches and Tehuelches adopted the Mapudungun as their main language (their own name is in Mapudungun). Together with Quechua, Aymara, Guarani and Nahuatl, Mapudungun was among the few Amerindian languages that extended their territories after the European arrival.

Mapuches that migrated to Patagonia lived often as nomads rising cattle or pillaging the Argentine countryside. The cattle stolen in the incursions (malones) would later be taken to Chile through the mountain passes and traded for goods, especially alcoholic beverages. The main trail for this trade was called Camino de los chilenos and run a length of about 1,000 kilometres (600 mi) from the Buenos Aires Province to the mountain passes of Neuquén Province. The lonco Calfucurá crossed the Andes from Chile to the Pampas around 1830 after a call from the governor of Buenos Aires, Juan Manuel de Rosas, to fight the Boreanos tribe. In 1859 he attacked Bahía Blanca in Argentina with 3,000 warriors. As in the case of Calfucura many other bands of Mapuches got involved the internal conflicts of Argentina until Conquest of the Desert. To counter the cattle raids a trench called Zanja de Alsina was built by Argentina in the pampas in the 1870s.