Historical novels, diaries, letters, monographs, and other published works can be excellent primary sources for use in your historical research. Depending on the time period you are researching, you might find them available freely on the web, or you may have to get them from a lending institution such as a library.
Many historical books are available online because they exist in what is called the public domain. If a work is in the public domain, this means its intellectual property rights, such as copyright, have expired, been forfeited, or are inapplicable. Many older works are available freely on the web.
The length of the period under which a work may be copyrighted depends on the laws of its country of origin. In the United States, for instance, material published before 1923 is in the public domain, while works published after that period are copyrighted for the author’s lifetime plus 70 years. Special copyright extensions may apply.
Project Gutenberg is an online library of books that exist in the public domain. Use it to find historical books on your research topic.