Nina Karin Monsen (born 29 May 1943) is a Norwegian moral philosopher and author.

She has written several books, both non-fiction and fiction, and has been active in Norwegian public debate since the early 1970s.

Monsen has a Magister's degree in Philosophy (1969) and was one of the founders of the Norwegian new feminist movement in 1970.

Her early work was on the logician Quine and she later studied feminist philosophy.

She has become the most visible proponent of Personalism in Norway, with Det elskende menneske (The loving human being, 1987) as her most central work.