región, central Chile, bordering Argentina to the east and fronting the Pacific Ocean to the west. It was given its present boundaries in 1974. Its area of 14,262 square miles (36,939 square km) includes the provincias of Ñuble, Concepción, Arauco, and Bío-Bío. The islands of Santa María, in the Bay of Arauco, and Mocha, 14 miles (23 km) offshore, are part of Arauco provincia. Bío-Bío región spans the coastal mountain range, the cool, fertile Central Valley, and the Andean cordillera. Bío-Bío región is drained in the north by the northwestward-flowing Itata River and its main tributary, the Ñuble River, and in the south by one of Chile's major rivers, the Bío-Bío, and its principal tributary, the Laja River.

When the Spaniards attempted to conquer the southern half of the región (the present provincias of Arauco and Bío-Bío), it was skillfully defended by the Araucanian Indians, who fiercely resisted the Spaniards near the town of Cañete in the 16th century. Not until the 1860s, some 50 years after Chile gained its independence from Spain, did the Chilean army pacify the Indians in this part of Araucanía. Only then was this Frontera (Frontier) territory widely settled, primarily by European immigrants but also by Chileans.

Most of the population is in the rural areas, and the region's economy is based upon diversified crops, timber trees, and mineral wealth. The chief crops are wheat, wine grapes, sugar beets, corn (maize), oats, and vegetables, cultivated in the Central Valley. Cattle and sheep are common in the open brush and forest range; pine forests yield lumber and tanning materials, and there are coastal fisheries. Concepción, the capital of the región, is economically important because of its mineral resources and industries. Near the coast at Coronel, Lota, and Penco, all served by railroad from Concepción, are coal and copper deposits. There is a large steel plant at Huachipato, near Talcahuano; other important economic activities in the región include textile manufacturing, flour milling, fish canning, sugar refining, and brewing. The Pan-American Highway, on which are located Los Angeles and Chillán, and the main north–south railroad pass through the central part of the región. Several resorts are on the coast. Pop. (1987 est.) 1,625,840.