The term “public domain” refers to creative materials that are not protected by intellectual property laws such as copyright, trademark, or patent laws. The public owns these works, not an individual author or artist. Anyone can use a public domain work without obtaining permission, but no one can ever own it.

Works fall into the public domain for three main reasons:

1. the term of copyright for the work has expired;

2. the author failed to satisfy statutory formalities to perfect the copyright or

3. the work is a work of the U.S. Government.

As a general rule, most works enter the public domain because of old age. This includes any work published in the United States before 1923. Another large block of works are in the public domain because they were published before 1964 and copyright was not renewed. (Renewal was a requirement for works published before 1978.) A smaller group of works fell into the public domain because they were published without copyright notice (copyright notice was necessary for works published in the United States before March 1, 1989)

As created works get older, they are defined as a public domain work. For a helpful chart that explains what qualifies as  public  domain can be found here.

• Open Access refers to resources that are freely available for viewing and/or use. Open Access is not the same as Public Domain, and most Open Access creators do retain their copyrights.
• Open Access is part of a continuum ranging from completely closed, subscription/purchase only access to completely open, no barrier publishing. Open Access is not related to the quality of materials or the peer-review/non-peer-review status of the publications.
• Open Access materials can be excellent resources to supplement online library materials. Many scholarly and peer-review journals have opened their back issues as open access, and others have converted partially or totally to open access for all issues.
• Open Access materials can often be used when copyright restrictions might prevent the use of "traditional" materials in an online setting. While Open Access materials are, for the most part, still under copyright by their creators, most academic and educational use is permitted without permission. Even if copying is not permitted, open materials can usually be linked from an online syllabus or reading list. Be sure to check the copyright or permissions statement before use.

Selected Sources for Open Access Resources

• ArXiv is an open access archive that is maintained and operated by Cornell University. It provides access to scholarly articles in the following disciplines: physics, mathematics, computer science, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics.
• DOAJ (Directory of Open Access Journals) is a directory that provides access to openly available peer-reviewed articles. It covers a wide range of disciplines.
• Google Scholar is a search engine that provides access to full text journal articles, preprints, e-books, and technical reports among other materials. It covers a wide range of disciplines.
• Open Access Button (OA plug-in and service) offers access to many aggregated repositories, open access journals, among other freely accessible legal sources.
• OSF Preprints (searches multiple preprint services) provides preprints in an open source environment.  It covers a wide range of disciplines.
• Pubmed Central is a U.S. National Institutes of Health (NIH) free digital archive of biomedical and life science journal literature.
• Unpaywall (OA plug-in and service) offers access to over 25,000,000 scholarly articles from OA journals and repositories.