Amanda Seyfried had a bad experience with Shiloh Fernandez at a dinner party, so Catherine Hardwicke had to persuade the actress to give him a chance.
According to the trailer, the story is set in the 1300s. No date is given in the film itself.
The novelization by Sarah Blakley-Cartwright is based on the shooting script rather than the finished film. The film's director, Catherine Hardwicke was friends with the book's author Sarah Blakely-Cartwright, and encouraged her to write a book based on the script before the film was released. Because of this, the book ended on a cliffhanger with Valerie confronting Peter in the woods, clearly not caring whether he is the wolf or not, leading to the two sharing a kiss before the book ends abruptly; this was to prevent spoiling the film's ending. This caused an outrage among readers who decried the abrupt ending and eventually the last chapter of the book was published after the film's release.
The character named Peter is from the Russian musical composition and children's story "Peter and the Wolf" written by Sergei Prokofiev in 1936.
Leonardo DiCaprio was a driving force behind this film being made, pushing for it to being greenlit in the first place and also collaborated in creating the story outline and writing the initial screenplay before it was rewritten, despite being ultimately uncredited. His Executive Producer credit remains.