From the Google Print Web site:
About Google Print
What is Google Print?
Google's mission is to organize the world's information, but much of that information isn't yet online. Google Print aims to get it there by putting book content where you can find it most easily - right in your Google search results.
How does Google Print work?
Just do a search on the Google Print homepage. When we find a book whose content contains a match for your search terms, we'll link to it in your search results. Click a book title and you'll see the page of the book that has your search terms, along with other information about the book and "Buy this Book" links to online bookstores (you can view the entirety of public domain books or, for books under copyright, just a few pages or in some cases, only the title's bibliographic data and brief snippets). You can also search for more information within that specific book and find nearby libraries that have it.
Where do these books come from?
The book content in Google Print comes from two sources: publishers and libraries.
There's lots more to learn at About Google Print, so check it out HERE. Then try out the service itself. Click HERE to link to Google Print.