尼曼河（立陶宛语：Nemunas；俄罗斯语：Неман；白俄罗斯语：Нёман；波兰语：Niemen；德语：Memel）发源于白俄罗斯的山区（在明斯克的西南部），流经白俄罗斯、立陶宛和俄罗斯，河长937公里，最后于克莱佩达注入波罗的海。

在俄语中，“德国人”为немец，即“尼曼河人”，因为在中世纪，德国人曾经占领过这个地区;在第二次世界大战之前，尼曼河代表德语分布地区的东部界限，例如在德国国歌歌词的第一段有这样的一句话，描述当时德意志民族的领土：「... von der Maas bis an die Memel....」（“从马斯河到梅梅尔”），但在第二次世界大战后，生活在尼曼河地区的德国人被流放到奥德河—现在的德国东部边界—以西。

The Neman, Nemunas, Nyoman, Niemen or Memel, a major Eastern European river, rises in Belarus and flows through Lithuania before draining into the Curonian Lagoon, and then into the Baltic Sea at Klaipėda. It begins at the confluence of two smaller tributaries (map coordinates 53.348194,27.108377), about 15 kilometers (9 mi) southwest of the town of Uzda in central Belarus, and about 55 km (34 mi) southwest of Minsk. In its lower reaches it forms the border between Lithuania and Russia's Kaliningrad Oblast. It also, very briefly, forms part of the border between Lithuania and Belarus. The fourteenth-largest river in Europe, the largest in Lithuania, and the third-largest in Belarus, the Neman is navigable for most of its 900 km (560 mi) length.