Seeking greater visibility for its Book Search engine, Google is making it easier for retailers, libraries and publishers to provide that service's capabilities on their own Web sites.

Via free code snippets and APIs (application programming interfaces), Google is allowing Web sites to display Book Search previews, most of which will allow potential buyers to browse up to 20 percent of a book's contents, Google announced on Monday.

Some retailers are already taking advantage of the program, including Books-A-Million, Blackwell Bookshop in the U.K., A1Books in India, Libreria Norma in Colombia, Van Stockum in the Netherlands and Livraria Cultura in Brazil.

Others planning to incorporate the Book Search functionality include Borders, Buy.com and Powell's Books. Several libraries, publishers and social book sites are also on board. Although aimed primarily at libraries, book retailers and publishers, the tools will be available to anyone who publishes a Web site.

Google has been scanning millions of books and making their contents available for searching through contractual agreements with publishers. It is these books that will provide most of the previews appearing on third-party sites.

Google also does wholesale scanning of some big library collections, including books that are in-copyright and in the public domain. Some of those in the public domain will also appear in the external site previews.

It's not surprising to see Google stay away from surfacing results obtained by scanning in-copyright books from library collections, since the practice has landed Google in court for alleged copyright infringement. When scanning library books, Google doesn't always seek the approval of copyright owners.

"What you'll see in the [Book Search] preview function are primarily books that are under contract with publishers because that's the nature of this program," said Tom Turvey, director of Google Book Search partnerships, in an interview.

Amazon.com isn't participating because the Book Search program provides functionality that Amazon.com already offers via its own Search Inside This Book capability, Turvey said.

"It's the retailers that don't want to invest millions of dollars to scan and host the books and so on that are the primary beneficiaries, as well as publishers," he said.

Amazon.com didn't immediately reply to a request for comment, but it's a safe bet that it's not happy with Google's move, which will allow Amazon.com competitors to rival its inside-the-book search.

Google is providing the Book Search tools and functionality free, and isn't generating any money from book sales commissions nor advertising, Turvey said. The main benefits for Google are broader exposure of Book Search and a strengthening of its book publisher partnerships, he said.