Test pages for an Amazon book subscription services surfaced earlier this week, hinting that the company would soon be launching its Oyster and Scribd competitor. Today, Kindle Unlimited has officially launched with a catalogue of 600,000 books (and more) for $9.99 a month.

Like we previously reported, the service offers a number audio books and ebooks found in Amazon's Prime Kindle Lending library like the Harry Potter series, the Hunger Games and Lord of the Rings. Reports suggest the Kindle Unlimited library may actually be a little bit more thorough and contains various Kindle exclusive titles. 

The Unlimited library, however, does still appear to be without offerings from the big 5 publishers, Penguin, Random House, Simon & Schuster, HarperCollins, Macmillan, and Hachette. This, as some have suggested, may be the thing that separates Oyster and Scribd from Amazon's new service, but the company is adding in some perks to sweeten the deal. Along with a 30 day free trial, subscribers will also get a free three month subscription to Audible as well.

After singing up, users will notice the Kindle Unlimited logo on titles included in the library along with a handy "Read for Free" button.

Currently the service is only available to those within the US, but Amazon said it plans to "expand this service to other countries. Please stay tuned."