Robert Ludlum wrote three Jason Bourne books. The first was The Bourne Identity, then there was The Bourne Supremacy and finally The Bourne Ultimatum (I may have the last two in the wrong order). I had never read them when I saw The Bourne Identity with Matt Damon. I liked the movie so I picked up the book. And I couldn't put it down. And when I finished, I had to get the other two. I ended up liking the books far more than I liked the movie, but with the exception of the name and a general resemblance to the story, the books are entirely different. Or, I guess I should say, the movie was not at all faithful to the book. I'm sure that the remaining movies will not have any relation to the books, but I'm hoping that they will at least be as good as the first movie.
If you liked the movie, I highly recommend that you give the books a try. And if you didn't like the movie, go ahead and give the book a try anyway. It is a different story.