Green wrote a book with another young adult novel writer called David Levithan, "Will Grayson, Will Grayson". It was published in 2010. It is about two boys who are both called Will Grayson. Half of the book is written from the perspective of Will Grayson 1. The other half is written by Will Grayson 2. Green wrote half of the book and Levithan wrote the other half.