The Directory of Open Access Books (DOAB) is a discovery service that indexes and provides access to scholarly, peer-reviewed open access books and helps users to find trusted open access book publishers. All DOAB services are free of charge and all data is freely available.
Google has partnered with more than 20,000 publishers and authors, and several major research libraries, to makes their publications discoverable through Google Books. While only limited text "snippets" can be viewed from books still protected by copyright, one can access the full text of many public domain books. Use the Advanced Search page to limit your search to full-text or public domain books. Books are available in PDF (.pdf) and ePub (.epub) formats.
The HathiTrust digital library offers a collection of millions of titles digitized via a partnership of academic & research institutions. Public domain titles are available for reading full-text. Copyright-protected works are searchable by their keywords. Full-book downloads are available to users from partner institutions; users from non-partner institutions are limited to page-by-page downloads.
The Internet Archive includes the full text of more than 2.5 million e-books, including e-books supplied by the Library of Congress. Books can be read online or downloaded and read in a variety of formats.
The National Academies Press (NAP) now makes all PDF versions of its books, currently nearly 10,000 titles, available for free download by users. NAP is the publisher for the National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council.
The Online Books Page is a large compilation of full-text literature resources on the Web, hosted by the University of Pennsylvania Libraries. The directory includes sections on general-purpose collections with substantial English-language listings (large-scale repositories; significant indexes and search aids; and significant smaller-scale archives), foreign language and literature resources, and specialty archives, including audio books and children’s literature. Formats vary.
E-books from the Internet Archive can also be found through Open Library, an Internet Archive initiative devoted to texts. Note: Audio books mentioned in OpenLibrary are generally only available to the blind or physically handicapped.
Many local libraries offer e-books to their users via the OverDrive subscription service. The libraries pay for this service for their users . Contact your local library about this and other e-book services offered free to library card-holders.