Karlsen is a Danish-Norwegian patronymic surname meaning "son of Karl" (\k(a)-rl\), an Old German given name. The form Carlsen is cognate. The parallel Swedish forms are Karlsson and Carlsson. People with the surname include:
Alexandria Karlsen (born 1978), American model, actress and author
Atle Karlsen (keyboardist) (?-), keyboardist of the Norwegian Rock band DumDum Boys
Geir Karlsen (born 1948), Norwegian footballer
Johan Sigurd Karlsen (1894–1967), Norwegian politician
Kari Karlsen (born 1952), Norwegian high jumper
Karl Henry Karlsen (1893–1979), Norwegian politician
Lars Olav Karlsen (born 1976), Norwegian actor
Morten Karlsen (born 1979), Danish footballer
Svend Karlsen (born 1967), Norwegian strongman
Tor Ottar Karlsen (born 1950), Norwegian politician