Public domain refers to creative works that are not protected by copyright. They belong to the public and can be used in any way without permission from the creator(s). Items can enter the public domain several ways:
- Copyright term has expired (see Copyright Term and the Public Domain in the United States for a helpful chart of copyright expiration dates) (1)
- The creator(s) failed to comply with copyright requirements at the time of publication or renewal
- Copyright never existed (ex: facts, short phrases, ideas, U.S. federal government documents*) (2) (3)
- The copyright owner(s) has dedicated the work to the public domain
It is important not to confuse public availability with public domain. The availability of a document online has nothing to do with its copyright status.
Finally, even though there isn't a legal requirement to cite public domain works, you should still do so as a matter of best practice. Not citing your sources could be considered plagiarism which can have severe professional and educational consequences.
Footnotes
1. In general:
- Items published in the US before 1927 are in the public domain
- Items published in the US between 1927 and 1964 and not renewed are in the public domain
- Works published without a copyright notice before March 1, 1989 are in the public domain
There are lots of exceptions to these general guidelines, so make sure you do your research on each item you are interested in.
2. 17 U.S. Code § 102 "In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
3. Not all federal government documents are in the public domain. Work by private individuals or contractors is frequently included in government documents through the use of a license. That work still has its own copyright.
