The seven Harry Potter novels are to be sold as e-books for the first time in October.
Author JK Rowling announced the series will also be available as audiobooks through a new website, Pottermore.
The interactive website will also feature new material which Rowling says she has been "hoarding for years".
"This is such a great way to give something back to the fans who made Harry Potter such a huge success," the author said.
The Harry Potter novels have sold more than 450 million copies through Bloomsbury in Britain, and Scholastic in the United States.
However the e-books - which will be available in several languages - will be published through Rowling's Pottermore Publishing, rather than her print publishers which do not own the digital rights.
Pottermore will go live on 31 July - Harry Potter's birthday.
Rowling told the BBC that the new material was being released online, rather than in a new book, because she did not have "a new story".
"Most of this writing is material I generated while I was writing the books initially," she said.
"It's background, and lots of details that didn't make it into the book.
"Some of it is new stuff in response to things fans have asked me over the years."
The site, which Rowling said she had been working on for two years, promises to immerse users in the boy wizard's world, offering opportunities for computer gaming, social networking and an online store.
Sections let users shop for wands in Diagon Alley, travel to Hogwarts from the imaginary platform at London's King's Cross train station and be sorted into Hogwarts' school houses using the Sorting Hat.
One million users will initially be chosen to help develop the online world, before it is open to all users from October.
Rowling told reporters at the London Pottermore launch she had no intention of writing an eighth Harry Potter book.
"I do have closure with Harry. I'm pretty sure I'm done on the novel front, but it was fun while it lasted," she said.