Sejny [ˈsɛi̯nɨ] (Lithuanian: Seinai) is a town in north-eastern Poland, in Podlaskie Voivodeship, close to the border with Lithuania and Belarus. It is located in the eastern part of the Suwałki Lake Area (Polish: Pojezierze Suwalskie), on the Marycha ("Seina" in Lithuanian from which the town bears its name) river, being a tributary of Czarna Hańcza.