Books in the public domain are generally those published before 1923. Think classics like
Treasure Island, Alice in Wonderland, Cicero, etc. as well as a wealth of primary and secondary sources for the humanities. There are many sources for public domain books. The best places to start are:
Project Gutenberg: http://www.gutenberg.org/
The oldest source for public domain books on the internet, Project Gutenberg has been transcribing and digitizing books since 1971.
“Project Gutenberg offers over 36,000 free ebooks to download to your PC,
Kindle, Android, iOS or other portable device. Choose between ePub, Kindle, HTML and simple text formats.”
Google Books: http://books.google.com/advanced_book_search
(be sure to click the button for “full view” to see free books)
Google Books offers both free and commercial eBooks. Like Project Gutenberg, the free books were generally printed before 1923. BE CAREFUL- many people are “re-publishing” books that are in the public domain and charging for them! Don’t pay money for
Treasure Island, The Three Musketteers or the like! If you are looking for a novel, you might want to start with the
current top free Google eBooks. Google Books is also an excellent source for pre-1923 non-fiction books that you can use as sources in research papers. You must do a specialized search to weed out the books that cost money as shown below: