Google said it had 3 million titles available from more than 4,000 publishing houses, including McMillan, Simon & Schuster and Random House, The New York Times reported.
It is a store set up for a world of gadgets and does not leave independent sellers out of the loop.
Customers can set up their own libraries, then access their purchases -- right at the sentence where they left off -- from a variety of devices, from mobile phones to home computers.
With the vast number of titles available and its dominant position as a search engine, Google will instantly be measured against established outlets, such as Apple, Amazon and Barnes & Noble.
The digital store that Google calls and "open ecosystem" also allows independent booksellers to sign on and connect from their own Web sites.
American Booksellers Association Chief Executive Officer Oren Teicher said, "This levels the playing field."
"If you want to buy e-books, you don't just have to buy them from the big national outlets," he said.