Usedom (Polish name Uznam) is an island north of the mouth of the Oder river, where it flows into the Szczecin Bay (ger: Stettiner Haff, pol: Zalew Szczeciński). It belongs to the region called Pomerania. Most of the island is a part of Mecklenburg-Western Pomerania, Germany (district Ostvorpommern), but the city of Świnoujście (ger: Swinemünde) at the eastern end of the island belongs to Poland since 1945. Area 445 km²; German part 373 km², Polish part 72 km². Population 76,500; German part 31,500; Polish part 45,000.

The island is nearly connected to the neighbouring island of Wollin. A very narrow strait leads the water from the Oder through the Szczecin Bay and into the Pomeranian Bay, which is part of the Baltic Sea. The strait between the island and the mainland is called Peenestrom; it is an extension of the Peene river, which flows into the westernmost part of the Szczecin Bay.

The main town on the island is Świnoujście, which has more inhabitants than the entire remaining island. The town giving its name to the German part is also called Usedom. The largest town in the German part is Ahlbeck. There are many popular tourist resorts at the northern coast, e.g. Ahlbeck and Zinnowitz. The probably best-known place on the island is the small village of Peenemünde, where the Wehrmacht tested their rockets including the V-1.