Rondônia is a state, about the size of Arizona, in the western Amazon Basin of Brazil. Rondônia borders Bolivia to its west and south; and the Brazilian states of Mato Grosso to its east, Amazonas to its north, and Acre to its northwest.

Rondônia was part of the state of Amazonas until 1943, when it became the territory of Guaporé, named for the river that separates it from Bolivia. It was renamed Rondônia in 1956 to honor Cândido Rondon (1865–1958), the Indian protector and explorer. In 1981, Rondônia became Brazil’s twenty-sixth and final state.

Prior to 1900, the region was occupied mainly by indigenous groups that included the Urueu-Wau-Wau, the Wayoró , and the Tupar&iacute. As the automobile industry grew, demand for rubber led settlers to the region to harvest latex from hevea brasiliensis trees. Called seringueiros, they tapped trees dispersed along trails through the tropical rain forest.

A complex, river-based trade system brought the rubber to Manaus and Belém was interrupted by series of waterfalls on the Rio Madeira. The eventual capital city of Porto Velho was established when U.S. and British investors built the Madeira–Mamoré Railroad to circumvent the waterfalls. The rubber boom ended when plantation-grown rubber was established in Asia.

Only 70,000 people lived in Rondônia in 1960, when POLONOROESTE began as a federal program to promote agriculture. An old telegraph road was paved and named BR-364, connecting Porto Velho to Cuiabá, Mato Grosso. Service centers were created near some of the old telegraph stations. Intended to attract 10,000 settlers, the paving of the road attracted nearly a half million migrants seeking farmland and gold. Crop yields from the tropical soils were low, leading many settlers to clear vast tracts of land before abandoning agriculture. Violence sometimes attended the consolidation of small farms into large ranches, while Rondônia experienced the highest rates of tropical deforestation in the world.

Beginning in the 1990s, service employment and inexpensive urban land continued to attract migrants. A majority of Rondônia’s 1.4 million people now live in cities and towns. Electricity is provided by imported diesel fuel and a large hydroelectric plant along the Rio Candeis. Proposals for additional hydroelectric plants on the Rio Madeira have led to renewed environmental concerns at the international level.