Świnoujście (ɕfinɔˈujɕt͡ɕɛ; Swinemünde ˌsviːnəˈmʏndə; Swienemünn; all three meaning "Świna [river] mouth"; Swina) is a city in Western Pomerania and seaport on the Baltic Sea and Szczecin Lagoon, located in the extreme north-west of Poland. Situated mainly on the islands of Usedom and Wolin, it also occupies smaller islands. The largest is Karsibór island, once part of Usedom, now separated by the Piast Canal, formerly the Kaiserfahrt, dug in the late 19th century to facilitate ship access to Szczecin.
Świnoujście directly borders the German seaside resort of Ahlbeck on Usedom, connected by a street and of beach promenade.
Since 1999, Świnoujście has been a city with powiat rights (miasto na prawach powiatu), within West Pomeranian Voivodeship. It was previously part of Szczecin Voivodeship (1975–1998). The city lies in the geographic region of Pomerania and had a population of 41,516 in 2012. Świnoujście is one of the most important areas of the Szczecin metropolitan area. The Świnoujście LNG terminal, opened in 2015, is located in the city. In 2023, the underwater Świnoujście Tunnel connecting the islands of Wolin and Usedom was opened.
Despite its relatively small population, Świnoujście is Poland's ninth-largest city by area.
The first human settlements in areas that are now Świnoujście appeared five thousand years ago, as confirmed by archaeological findings. For a thousand years, the estuary of the river was part of the state of the Świnoujście, included in the emerging Polish state in the 10th century by first Polish ruler Mieszko I.
In the early 12th century, the island became part of the Duchy of Pomerania, founded as a vassal duchy of Poland. In later centuries, local Pomeranian princes ruled the area, and on both sides of the river, they built fortified castles, which were destroyed several times by the Danish invasions in the 12th century, in 1170 and 1173. Between 1185 and 1227, the settlement was part of a Danish fief.
During the Thirty Years' War (1618–1648) the city became part of the Swedish Empire.