Congo River, a river of equatorial Africa and one of the great rivers of the world. Its discharge of water to the sea is second only to that of the Amazon. Measured from the source of its principal headstream, the Lualaba River in the Democratic Republic of the Congo, the Congo River is about 2,900 miles (4,700 km) long and drains an area of some 1,500,000 square miles (3,900,000 km2). The river begins in southeastern Democratic Republic of the Congo and flows northward and westward in a giant arc through tropical savannas and rain forests to the Atlantic Ocean. It drains virtually all of the Democratic Republic of the Congo, the largest and most populous nation in the river's basin, and parts of eight other countries.

The Congo is a primary transportation route in central Africa, where other means of transport are poorly developed. Matadi is the main seaport; Kinshasa, Mbandaka, and Kisangani are among the numerous river ports. The Congo also provides large amounts of hydroelectric power.

Diogo Cão, was the first European to discover the mouth of the Congo, in 1482. For almost 400 years, however, the course of the river remained unknown. David Livingstone, a British missionary, reached the upper Lualaba and the headwaters region in the late 1860's. The Congo's entire course became known when the journalist-explorer Henry M. Stanley descended the river from its upper reaches to its mouth in 1876–77.