river formed on the Cumberland Plateau by the confluence of Poor and Clover forks in Harlan county, southern Kentucky, U.S. Looping through northern Tennessee, it joins the Ohio River after a course of 687 miles (1,106 km) at Smithland, Ky., 12 miles (19 km) upstream from the mouth of the Tennessee River. From its headwaters to the Cumberland (or Great) Falls, in Whitley county, Ky. (site of a state park), the river is a mountain stream that is of little volume during late summer but is subject to heavy floods during winter and spring. From Williamsburg, Ky., above the falls, to the Kentucky–Tennessee state line, the Cumberland crosses a highland bench in the Cumberland Plateau and flows in a gorge between cliffs 300–400 feet (90–120 m) high. Thence the river enters the central limestone basin of Tennessee and, turning north, crosses the plain of western Kentucky to the Ohio River. At one point it is less than 2 miles (3 km) from the lower Tennessee River. The Cumberland's drainage area is 18,080 square miles (46,830 square km).

The Cumberland's chief tributaries, all entering downstream from the falls, are the Laurel, Rockcastle, and South Fork in Kentucky; the Obey, Caney Fork, Stones, Harpeth, and Red in Tennessee; and the Little River in western Kentucky. Nashville, Tenn., is the largest city along the river. Other centres include Pineville, Barbourville, and Williamsburg in eastern Kentucky; Carthage, Clarksville, and Dover in Tennessee; and Eddyville in western Kentucky.

The development of a series of lakes on the Cumberland took place as part of the Tennessee Valley Authority (TVA) system. Wolf Creek Dam (1952) for flood control and power, in Russell county, Ky., created Lake Cumberland, which extends to the base of Cumberland Falls. Large power dams are in operation on two tributaries: Dale Hollow Dam (1953) on the Obey River near Celina, Tenn.; and Center Hill Dam (1951) on Caney Fork, southeast of Carthage. Old Hickory Dam, upstream from Nashville, ponds the water to Carthage, the head of navigation on the river. Cheatham Dam is upstream from Clarksville. Barkley Dam (in operation since 1966) controls the lower river.

Fort Donelson National Military Park, in northern Tennessee on the Cumberland, commemorates the American Civil War battle that opened the Tennessee River to Union troops.