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 Swinoujscie (German name: Swinemünde), which has more inhabitants than the entire remaining island. The largest town of the German part is also called Usedom. 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.