Alsen may refer to:
Places Als Island, Denmark; called Alsen under Prussian/German administration (1864–1920) Alsen, North Dakota, US Alsen, South Dakota, US Alsen, Sweden, a parish and former municipality in Jämtland County, Sweden Alsen, a hamlet in Catskill, New York, US
People Herbert Alsen (1906–1978), German operatic bass Elsa Alsen (1880–1975), Prussian-born American operatic soprano