Is there a book to letters Juliet?

You're probably thinking of the movie "Letters to Juliet" which is based on the novel "Letters to Juliet" by Lise Kogman.

There is no actual "book to letters Juliet" as the movie is a fictional story. However, in the movie, Juliet's balcony in Verona, Italy, is a real place where people leave letters to Juliet.

If you're interested in the story of "Letters to Juliet", you can read the novel by Lise Kogman.