Right now, many of our books are provided either by publishers and authors, through the Google Books Partner Program, or by our library partners, through the Library Project. We've also added metadata records for a great many books to the Google Books index.
The Partner Program is an online-book marketing program designed to help publishers and authors promote their books. Publishers and authors send us their books and we digitally scan them and make them findable in our search results - all for free. For the most part, you can browse through a number of pages of these books, typically about 20%.
The Library Project involves partnerships with several libraries to include their collections in Google Books. Books scanned through the Library Project are displayed to you like a card catalog, including basic info about the book, and in some cases basic info plus a few snippets - sentences of your search terms in context. When these books are in the public domain, we'll display the full text of the book, from start to finish.
In order to make Google Books a more comprehensive book discovery tool, we felt that it was necessary to include results for books that we hadn't yet digitized at our library partners or received via our Partner Program. Since we haven't scanned these books, they're not full-text searchable. This means they'll only be searchable by title, author, subject or copyright information, and in some cases, tables of contents and/or a book summary. In effect, this is like seeing a library card catalog online. However, for each book's "About this book" page, where possible, we'll include reviews, articles that cite the book, books that cite the book, and related books.