The Vistula ( /ˈvɪstʃələ/; Polish: Wisła [ˈvʲiswa], German: Weichsel) is the longest and the most important^{[citation needed]} river in Poland, at 1,047 km (651 miles) in length. The watershed area of the Vistula is 194,424 km² (75,068 sq mi), of which 168,699 km² (65,135 sq mi) lies within Poland (splitting the country in half).

The Vistula rises at Barania Góra in the south of Poland, 1220 meters above sea level in the Silesian Beskids (western part of Carpathian Mountains) where it begins with the White Little Vistula (Biała Wisełka) and the Black Little Vistula (Czarna Wisełka). It then continues to flow over the vast Polish plains, passing several large Polish cities along its way, including Kraków, Sandomierz, Warsaw, Płock, Włocławek, Toruń, Bydgoszcz, Świecie, Grudziądz, Tczew and Gdańsk. It empties into the Vistula Lagoon or directly into the Gdańsk Bay of the Baltic Sea with a delta and several branches (Leniwka, Przekop, Śmiała Wisła, Martwa Wisła, Nogat and Szkarpawa).

The name was first recorded by Pliny in AD 77 in his Natural History. He uses Vistula (4.52, 4.89) with an alternative spelling, Vistillus (3.06). The Vistula River ran into the Mare Suebicum, which is today known as the Baltic Sea. The root of the name Vistula is Indo-European ultimately from proto-Indo-European. The diminutive endings -ila, -ula, were used in many Indo-European language groups, including Latin (see Ursula).