At the 2015 Digital Book World conference, Amazon SVP Russ Grandinetti said he was “cautiously optimistic” about the prospects for Kindle Unlimited, the subscription service which Amazon had launched six months earlier. Whatever fears Grandinetti may have had were evidently unfounded.

Kindle Unlimited, which turns 10 this year, has been a huge success for Amazon. To mark the anniversary of the service, Amazon has released selected insights, starting with what it says is the fact that more than three billion books have been read via Kindle Unlimited in the decade since its launch. The service has always featured a mix of books from traditional trade publishers and self-published authors using the Kindle Direct Publishing program; one stat that Amazon regularly shares is the money it has paid to KDP authors. Over the 10 years Kindle Unlimited has been active, Amazon said KDP authors have earned more than $3.5 billion from the KDP Select Global Fund and All Star Bonus pools. Nearly $650 million has been earned by KDP authors in just the last 12 months.

While some traditional publishers had initially expressed concerns about subscription services in general a decade ago, today Kindle Unlimited has a catalog of more than 4 million titles that includes e-books, audiobooks, and magazines. Recent additions, said Tracy Schultz, director of reading subscriptions at Amazon, include Fourth Wing by Rebecca Yarros, Freida McFadden’s thriller The Housemaid, and Gregg Olsen’s true crime story If You Tell. As part of its 10th anniversary, the service has added a new selection of popular books, including Weyward by Emilia Hart, After I Do by Taylor Jenkins Reid, and The Long Walk by Stephen King.

The current subscription fee is $11.99 per month and members can read and hold up to 20 titles at a time before returning them.

Also to mark the anniversary, Amazon has highlighted some of the most-read titles on Kindle Unlimited from the past decade. Freida McFadden proved a Kindle Unlimited favorite, and the books on the list come from a mix of traditional publishers, Amazon Publishing, and self-published authors. The most-read titles are:

  • The Harry Potter series by J.K. Rowling
  • The Housemaid by Freida McFadden
  • Things We Never Got Over by Lucy Score
  • Reminders of Him by Colleen Hoover
  • Haunting Adeline by H. D. Carlton
  • Regretting You by Colleen Hoover
  • The Housemaid's Secret by Freida McFadden
  • If You Tell by Gregg Olsen
  • Never Lie by Freida McFadden
  • The Handmaid's Tale by Margaret Atwood

By genre, some of the most read-books on Kindle Unlimited in the U.S. are:

  • Romance: Things We Never Got Over by Lucy Score
  • Literary fiction: Beneath a Scarlet Sky by Mark Sullivan
  • Mystery/Thriller: The Housemaid by Freida McFadden
  • Sci-Fi/Fantasy/Horror: The Handmaid's Tale by Margaret Atwood
  • Nonfiction: If You Tell by Gregg Olsen

“We are thrilled by the success of Kindle Unlimited over the last 10 years and how it’s performed for both readers and authors – it just keeps getting better for our millions of subscribers," said Schultz. "As we reach this 10-year milestone, we remain committed to continually enhancing the Kindle Unlimited experience to make sure our members can always find a book they will love to read.”