Als (äls) [key], Ger. Alsen, island, 121 sq mi (313 sq km), Sønderjylland co., S Denmark, in the Lille Bælt, separated from the mainland by the narrow Alensund. Sønderborg (partly situated on the mainland) is the main city; other towns include Augustenborg and Nordborg. Farming (particularly of apples and grain), fishing, dairying, and manufacturing (especially of motor vehicle parts) are the main occupations. Danfoss, a company that produces heating and refrigerating plants is there. Its beautiful beaches make the island a popular tourist attraction. It was held by Germany from 1864 to 1920.