Summer reading season just got a little cheaper.

Amazon is offering a 30-day free trial to Kindle Unlimited for Prime Day, giving readers a chance to browse millions of e-books, audiobooks, comics and magazines without paying upfront. Don’t have a Kindle e-reader? Shop these Kindle Prime Day deals here.

Kindle Unlimited is Amazon’s all-you-can-read digital subscription service. Instead of buying e-books individually, members pay a monthly fee — typically $11.99 per month — to borrow from a rotating library of more than 4 million titles. You do not need to own a Kindle device to use it; books can be read through the free Kindle app on a phone, tablet, computer or e-reader.

The easiest way to think about Kindle Unlimited is as a streaming-style library for books. You do not own the titles permanently, the way you would if you bought a Kindle book outright. Instead, you borrow eligible books, keep them in your digital library while your subscription is active, and return them when you are done. It is especially useful for readers who go through multiple books a month, or who tend to read heavily in categories where Kindle Unlimited is strongest: thrillers, romance, fantasy, celebrity memoirs, self-help and BookTok favorites.

The biggest draw is the catalog. Kindle Unlimited has become a major destination for viral genre fiction. Freida McFadden’s “The Housemaid,” one of the most talked-about psychological thrillers of the past few years, is included in Kindle Unlimited, along with other McFadden titles such as “The Housemaid’s Secret” and “Never Lie.”

Romance readers will also find plenty to binge. Lucy Score’s “Things We Never Got Over” has been one of Kindle Unlimited’s biggest BookTok-era success stories, while Colleen Hoover titles have also been among the most-read books on Kindle Unlimited over the years, including “Reminders of Him” and “Regretting You.”

Sign up for a free trial to Kindle Unlimited here.