Amazon has made Kindle eBooks available to users of the iPhone and iPod Touch.
It began selling 240,000 eBook titles through the Apple App Store yesterday, Amazon said. Owners of both a Kindle and an iPhone will be able to access their purchases from both devices.
Amazon has also added features such as the generation of automatic bookmarks, which will be automatically updated across all devices.
Last month, Amazon shipped a new version of its Kindle eBook reader, capable of storing up to 1,500 titles - compared to the original model's 200.
Amazon's VP in charge of the Kindle, Ian Freed, told the New York Times the company does not expect the move to eat into hardware sales, and sees the offerings as complementary.
Google recently announced it was working to optimize its public domain book catalog for viewing on mobile devices.