The Neman, Niemen, Nioman, Nemunas or Memel is a river in Europe that rises in central Belarus and flows through Lithuania then forms the northern border of Kaliningrad Oblast, Russia's western exclave, which specifically follows its southern channel. It drains into the Curonian Lagoon, narrowly connected to the Baltic Sea. It flows about 937 km (582 mi), so is considered a major Eastern European river. It flows generally west to Grodno within 12 kilometres (7.5 mi) of the Polish border, north to Kaunas, then westward again to the sea.

The largest river in Lithuania, and the third-largest in Belarus, it is navigable for most of its length. It starts from two small headwaters merging about 15 kilometers (9 mi) southwest of the town of Uzda – about 55 km (34 mi) southwest of capital city Minsk. Only 17 kilometres (11 mi), an eastward meander, contributes to the Belarus–Lithuania border. Thereafter the river includes notable loops along a minor tectonic fault.

Its drainage basin settled in the late Quaternary to be roughly along the edge of the last glacial sheet so dates to about 25,000 to 22,000 years BC. Its depth varies from 1 meter (3 ft 3 in) in its upper courses to 5 meters (16 ft) in the lower basin.