Eupen (oiˈpən) [key], town (1991 pop. 17,161), Liège prov., E Belgium, on the Vesdre River, near the German border. It is a center for the manufacture of soap, beer, and cables. Nearby is a major hydroelectric station. The districts of Eupen and Malmédy (c.380 sq mi/980 sq km) were awarded (1815) to Prussia by the Congress of Vienna. Strategically important for the defense of Belgium, the districts were transferred (1919) to Belgium under the terms of the Treaty of Versailles. Their population is predominantly German-speaking. During World War II the districts were temporarily annexed (1940–44) by Germany.