Book stuffing is a term that encompasses a wide range of methods for taking advantage of the Kindle Unlimited revenue structure. In Kindle Unlimited, readers pay $9.99 a month to read as many books as they want that are available through the KU program. This includes both popular mainstream titles like the Harry Potter series and self-published romances put out by authors like Crescent and Hopkins. Authors are paid according to pages read, creating incentives to produce massively inflated and strangely structured books. The more pages Amazon thinks have been read, the more money an author receives.