I first learned about "Kristin Lavransdatter" through the movie, directed by Liv Ullmann. It is in Norwegian with English subtitles. We watched it at a Daughters of Norway meeting, and I enjoyed it so much I rented it and watched it again a few months later.
I recently read the first two books in the trilogy by the Norwegian author and Nobel Laureate, Sigrid Unsdet, "The Wreath" and "The Wife" and plan to read "The Cross". The story is set in fourteenth century Norway and was inspired by Icelandic Sagas.
Like any book made into a movie, there are big differences between the two. First, the movie leaves off at the end of "The Wreath", while the books continue to tell the story of Kristin's whole life. The film is a beautiful, dramatic romance. The books have a different feeling, the background of Norway's history and every-day life have just as much presence as Kristin's life.
The trilogy is so detailed and gives a view into medieval Norwegian life, how people lived and thought. The movie is so rich and beautiful. I highly recommend both.