Why isn't there a rating system for books?

As a school aged person and in college, I hated to read. I think it was because I was told what to read and when. But now, as an adult, I've begun to enjoy reading for fun. I have found a few authors that I like (some Christian some not). But wanting to be somewhat diversified in my reading, I have tried to venture out of my "comfort zone" and read other genres and authors.

However, as I have begun shopping for new books to read during the summer time (like at Barnes & Noble or Waldenbooks) I have noticed that you can't judge a book by its cover. I try, while shopping, to find books that seem to be interesting and good...but once I bring them home...they are often filled with nothing but filth (foul language, sexually explicit material...).

So my question is if we have a rating system for movies and music, and (even now with the V-chip) TV shows...why is there no rating system for books?

Is this too far out there? Someone tell me what you think.

 

Thank you for the information. I'll try to use it.

However, I am still wondering why there isn't a national system (like G, PG, PG-13...).????