Amazon has acquired Goodreads.com, a Web site featuring user-generated reviews of books. The purchase comes amid mounting rumors that Goodreads, which CEO Otis Chandler launched in 2007, might start selling books directly from its site.

Goodreads, which is one of the most popular among a raft of sites created as a book recommendation engine--members are directed to titles by seeing what their friends are reading, or have recommended--does not currently sell any books, but many in the industry saw it as an ideal sales outlet.

The details of the purchase, which is set to close in the second quarter of 2013, were not disclosed by Amazon, but the retail giant confirmed that Goodreads will remain headquartered in San Francisco. The site currently has over 16 million members, averages 37 million unique visitors a month, and has over 30,000 book clubs.

When asked how Goodreads would be integrated into Amazon, and the all-important question of how, and when, a retail component might be rolled into the site--currently users can buy books through a host of third party retailers, including Amazon--both Chandler and Russ Grandinetti, Amazon v-p, Kindle content, skirted the subject. When pressed, Chandler said: "We don't have any plans to change anything about the buy links in the short term, but in the long term we're going to do what's best for our users."

Grandinetti said the acquisition was "not about making Goodreads commerce enabled," but, instead, about opportunities to improve the user experience of Kindle owners. Chandler said the site will remain "an independently controlled subsidiary of Amazon" and noted it will keep "full control of editorial content and the recommendations."

Peter Hildick-Smith, president of the market research firm Codex Group, said the company's March 1 study shows that many Goodreads users also like Amazon. The study found that among past month book buyers, 36% rate Amazon.com as “one of my favorite brands”--more than twice as popular as John Grisham, who rated 17% on the same scale -- but among past month book buyers who visited GoodReads at least once in the last week, that number jumps to 45% rating Amazon.com as “one of my favorites”, or nearly half of GoodReads visitors.

Additionally, 30% of GoodReads visitors already have a Kindle eReader in their home, while 24% of all other past month book buyers do. While the digital reading device currently most owned by GoodReads visitors is the Apple iPad, it’s at the same ownership level as all other book buyers. "Overall," Hildick-Smith said about the deal, "it looks like a very attractive fit for Amazon and its book buying fans."

This is the second book recommendation site that Amazon has bought ouright. In 2008 it acquired Shelfari, but there seems to be no plans to integrate Shelfari and Goodreads. It also owns a piece of LibraryThing.

To ease any misgivings Goodreads's biggest supporters might have about the deal, the site e-mailed the following letter to its most ardent users, called "librarians," shortly after the purchase was announced:

Today is a very big day for all of us at Goodreads. As you may have seen on our blog, we are joining the Amazon family.

We greatly appreciate all you do as a Goodreads Librarian so we wanted to reach out to you individually since you play an important role in our community.

You’ll be glad to know that this announcement is great news for our catalog. Amazon metadata will be returning to the site, and we will have an even more comprehensive record of self-published books, as well as more complete records of international books. We will continue to link to a variety of sites on our book pages, of course, including OCLC WorldCat for library data. All of your reviews and ratings will remain on Goodreads.

By joining the Amazon family, the Goodreads team will be able to invest more in the things that our members care about. We’ll also be working together on inventing new services for readers and authors. As part of this, we’ll be increasing the size of our team over time, and will be able to add lots of great new features that members and librarians will be excited about!

I can’t make this clear enough – we plan to continue growing Goodreads and investing in making it a great community for librarians, and everyone else.

We said in our blog post that our team gets out of bed every day motivated by the belief that the right book in the right hands can change the world. Now Goodreads can help make that happen in an even bigger and more meaningful way as part of the Amazon family.

Here’s to the next chapter!

Otis, Elizabeth, and the Goodreads Team