More and more e-books are being made available for free online. This may be through the digitisation of out of copyright books, such as via Project Gutenberg, or reputable academic publishers providing 'Open Access' e-books for more recently published works. This page points towards some of the main providers of free online books. As well as going direct to these providers to perform your search, you may also perform a search engine search for the book you need, possibly including the name of the e-book provider (e.g. 'renaissance Italy internet archive').
While there isn't one comprehensive place to find all open access and freely available e-books, Google Scholar might be a good place to start your search.
Many open access publishers and content providers, such as Open Access Publishing in European Networks (OAPEN) and JSTOR work with Google Scholar to make their content discoverable.
If you're interested in a specific topic or non-English e-books, you may find the index maintained by the University of Pennsylvania helpful. It provides links to major sources of free e-books, including books digitised in non-English speaking countries.
The OAPEN Library contains freely accessible academic books, mainly in the area of Humanities and Social Sciences.
HathiTrust is a collection of millions of titles digitized from libraries around the world.
Below you can find details of some of the most well-known freely available e-book collections. You will also find a link to a longer list of e-book collections.
The Directory of Open Access Books provides access to open access books published by a variety of publishers, across a range of disciplines.
Project Gutenberg contains over 60,000 free e-books. These are typically digitized versions of books that were published long ago and for which any US copyright has expired. Mainly literary works and reference items of historical significance.
The Internet Archive contains more than 8 million e-books which are in the public domain.
Digitised versions of books, which are fully searchable. You might see a percentage of pages from the book, or even the entire book, depending on the wishes of the rightsholder, or if the book is out of copyright.