Usedom (Usedom ˈuːzədɔm, Uznam ˈuznam) is a Baltic Sea island in Pomerania, divided between Germany and Poland. It is the second largest Pomeranian island after Rügen, and the most populous island in the Baltic Sea.
It is north of the Szczecin Lagoon estuary of the Oder river. About 80% of the island belongs to the German district of Vorpommern-Greifswald in the state of Mecklenburg-Vorpommern. The eastern part and the largest city on the island, Świnoujście, are part of the Polish West Pomeranian Voivodeship. The island's total area is – in the German part and in the Polish part. Its population is 76,500 (German part 31,500; Polish part 45,000).
With an annual average of 1,906 hours of sunshine, Usedom is the sunniest region of both Germany and Poland, and it is also one of the sunniest islands in the Baltic Sea, hence its nickname "Sun Island" (Sonneninsel, Wyspa Słońca).
The island has been a tourist destination since the Gründerzeit in the 19th century, and features resort architecture. Seaside resorts include Zinnowitz and the Amber Spas in the west, the Kaiserbad and Świnoujście in the east.
The island is separated from the neighbouring island of Wolin to the east by the Strait of Świna, which is the main route connecting Szczecin Bay with the Pomeranian Bay, a part of the Baltic Sea. The strait between the island and the mainland is called the Peenestrom; it is a downstream extension of the valley of the Peene river, which flows into the westernmost part of the Szczecin Lagoon. The island is mostly flat, partly covered by marshes.
Geographical features include a number of lakes:
The largest town on the island is Świnoujście, which has a total population of 41,500. The western part of Świnoujście covers the entire Polish part of the island. Another town, Usedom, gives its name to the island. The largest municipalities in the German part are Heringsdorf (from 2005 to 2006 called Dreikaiserbäder, literally "The Three Imperial Spas") and Zinnowitz.