The Belarus–Lithuania border is an international border almost 678.8 km (421.8 mi) in length between the Republic of Belarus and the Republic of Lithuania. It is an external border of the European Union as well as the western border of the Commonwealth of Independent States. 379.9 km (236.1 mi) of the border is on land, while 298.9 km (185.7 mi) are on water, crossing lakes, e.g. Lake Drūkšiai and following some rivers, e.g. Dysna River and Neman River.

The Neman, Niemen, Nyoman, 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. The 937 km (582 mi) long Neman is 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.