The $399 Kindle, which weighs 10.3 ounces, lets users browse Amazon's online store, download and pay for a book directly through the device and then read the downloaded book.

"Whether you're lying in bed or riding a train, you can think of a book, and have it in less than 60 seconds," Chief Executive Officer Jeff Bezos said in a letter on the retailer's Web site.

Kindle also lets users download songs, like Apple Inc. (NASDAQ:AAPL)'s iPod portable media player, although Amazon does not let customers buy music directly from its store through Kindle.

Amazon said it currently had 90,000 books, blogs, magazines and newspapers for sale.

Best-selling books and new releases cost $9.99, compared with roughly $13 to $20 for hardcover bestsellers.

Newspapers cost $5.99 a month to $14.99 a month, while magazines range from $1.25 to $3.49 a month. Blogs start at 99 cents a month, Amazon said.

The device, whose "e-ink" technology is intended to be easier on the eyes than a traditional computer display, can hold 200 books and remain on for 30 hours between charges, Amazon said.

Its keyboard is currently intended for taking notes.