Google guide

The advantages:

• access to free, public domain ebooks
• you're searching Google's database of books rather than websites searched by Google
• it's a good "discovery tool" - if the book is out of copyright, or the publisher has given permission, you'll be able to see a preview of the book, and in some cases the entire text. If it's in the public domain, you can read the full book
• it can help you identify journals and/or authors that cover your topic
• you can search the fulltext of the books - use “Search in this Book” to narrow or focus your search on more specific terms
• you can retrieve both books and articles in a single search

The limitations are:

• your results will include children's books
• you can't sort the results i.e. you cannot limit to fiction only
• it's not helpful for accessing current/popular books (copyright issues) 
• the quality of reproduction in digitization can be inconsistent
• not everything is full text - search our library catalogue or request the book via Interlibrary loan

What are you allowed to see in Google Books?

Google Book Search works just like their web search. When they find a book with content that contains a match for your search terms, you'll see a list of search results. You might see a few snippets - sentences of your search term in context. If a publisher or author has given Google permission, they decide whether to make their books fully or partly viewable. You may see a full page and be able to browse within the book to see more pages.

If a book is out of copyright, you'll see a full page and you can page forward or back to see the full book. Clicking on "Search within this book," allows you to perform more searches within the book you've selected.

See Book search help from Google for more information.