Ellefsen is a surname. Notable people with the surname include: Gunnar Ellefsen (1930–1997), Norwegian politician for the Labour Party Håvard Ellefsen (born 1975), Norwegian electronic musician best known as Mortiis Harald Ellefsen (born 1950), Norwegian politician for the Conservative Party Henrik Ellefsen (born 1971), Norwegian businessman Pauli Ellefsen (born 1936), Faroese politician and member of the Union Party Norwegian-language surnames