The Obion River system is the primary surface water drainage system of Northwest Tennessee.

The Obion is comprised of four major forks, the North Fork, Middle Fork, South Fork and Rutherford Fork (the last being named for the town of Rutherford). The conflunces of these forks is only a few miles above the mouth of the Obion into the Mississippi River; for by far the majority of their lengths they are separate streams.

In the mid-20th century, the Obion system was largely channelized for agricultural purposes, under the auspices of the Obion-Forked Deer Basin Authority, a Tennessee state agency which coordinated this work with the United States Army Corps of Engineers. Some of the results of channelization included increasing erosion, loss of wildlife habitat, and increased flooding downstream. Now this process has been halted, and, in a few places, even somewhat reversed, with the restoration of wetlands.

The origin of the name "Obion" is somewhat controversial, with some contending that it derives from a Native American word and others that it represents a corruption of the name of an Irish trapper, O'Bion or, perhaps, O'Brien.

Obion County, Tennessee is named after the Obion River.