South American Indian people of eastern Bolivia. They live in the dense tropical forests of the eastern and northern parts of the department of Beni. Unlike other Indians of the Chiquitos-Moxos region, the Sirionó are linguistically Tupians (q.v.) who long ago became separated from the main group of Tupian-speakers through migration; their traditional seminomadic culture was less complex than those of their neighbours. Early efforts by missionaries and government agents to settle them on the land proved disastrous, and their numbers were reduced by disease. At the beginning of the 21st century most of the approximately 500 remaining Sirionó had either withdrawn into the deep forest or were providing labour on farms and cattle ranches.

Sirionó subsistence needs were traditionally met through a combination of farming, hunting, and gathering. In the dry season they planted corn (maize), sweet potatoes, and sweet cassava; then they left their fields for a nomadic period of hunting and gathering, returning only for short intervals to care for their crops. The harvest season brought them back to clear their fields and store the crop, after which they resumed their migratory life.

Their traditional material culture and social organization were simple. They carried fire from camp to camp, saying that they had lost the art of making it. Their temporary huts, built of poles covered with palm leaves, were sometimes large enough to shelter 120 people. They traced their descent through the maternal line, and the married couple lived in the wife's village or band. They believed in spirits but lacked shamans to intercede with them. They made beer out of maize and wild honey; among their pastimes were dancing and singing. They wore no clothes but painted their bodies.