What is is 500 days of summer a book?

500 Days of Summer is a 2009 American romantic comedy-drama film directed by Marc Webb and starring Joseph Gordon-Levitt and Zooey Deschanel. It is not a book, but rather an original screenplay by Scott Neustadter and Michael H. Weber. However, there is a novelization of the movie written by Rebecca Serle, which was released in 2009. The book is a retelling of the story in novel form, and includes additional details and insights into the characters and their motivations.