More details from the Amazon Harry Potter e-book page
Harry Potter Kindle books are now available on Kindle! All seven books in the series can be purchased at J.K. Rowling's Pottermore Shop, a third-party site. Clicking on "Buy at Pottermore" will take you to Pottermore Shop, where you will need to create a separate account. Like all Kindle books, books purchased from Pottermore are "Buy Once, Read Everywhere" and will be delivered to your Kindle or free Kindle reading apps.