Google is making the leap from digital librarian to merchant in a challenge to Amazon.com and its electronic reader, the Kindle.
The long-awaited Internet book store opening today in the US draws upon a portion of the 15 million printed books that Google has scanned into its computers during the past six years.
About 4,000 publishers are also allowing Google to carry many of their recently released books in the new store.
Google says those publishing deals will ensure that most of the current best sellers are among the 3 million e-books initially available in the new store.
Millions more out-of-print titles will appear in Google's store, called eBooks, if the company can gain federal court approval of a proposed class-action settlement with US publishers and authors.