|“||describes intellectual property that is freely available to everyone. Proof that something is already in the public domain is an absolute defense against the assertion of any exclusive IP right such as a patent or copyright.||”|
U.S. copyright law
|“||[is a] work of authorship that is not protected by copyright. . . . In the United States, a copyrighted work enters the public domain when its full copyright term has expired. In addition, works published in the United States without a copyright notice on or before March 1, 1989 may be in the public domain, and works registered or published in the United States on or before December 31, 1963 may be in the public domain if the copyright was not renewed in a timely manner. The status of a creative work which, through expiration of term or failure to comply with statutory formalities, is not protected by copyright.||”|
|“||consist[s] of works that are either ineligible for copyright protection or with expired copyrights. Public domain refers to the total absence of copyright protection for work The public domain is a range of abstract materials commonly referred to as intellectual property which are not owned or controlled by anyone. The term indicates that these materials are therefore 'public property,' and available for anyone to use for any purpose.||”|
Overview (U.S. copyright law)
The term "public domain" is an often misunderstood and misused term. Generally it means that the material is not protected by copyright. There are three situations in which a work will be in the public domain: (i) a work for which copyright protection was never available; (ii) a work for which copyright protection was never properly secured, and (iii) a work for which copyright protection has expired or has otherwise been lost.
Effect of the public domain
"[T]he bedrock principle of copyright law [is] that works in the public domain remain there." "[O]nce the . . . copyright monopoly has expired, the public may use the . . . work at will and without attribution." "These imaginative works inspire new creations, which in turn inspire others, hopefully, ad infinitum. This cycle is what makes copyright 'the engine of free expression.'" 
Overview (U.S. patent law)
"Congress may not authorize the issuance of patents whose effects are to remove existent knowledge from the public domain, or to restrict free access to materials already available."
- Defense Acquisition University, ACQuipedia, Intellectual Property and Data Rights (full-text).
- Compendium of U.S. Copyright Office Practices, Third Edition, Glossary, at 13-14.
- Public domain definition
- Golan v. Holder, 565 U.S. 1, 132 S. Ct. 873, 878 (2012) (full-text).
- See Golan v. Gonzales, 501 F.3d 1179, 1187 (10th Cir. 2007) (full-text).
- Dastar Corp. v. Twentieth Century Fox Film Corp., 539 U.S. 23, 33-34 (2003) (full-text).
- Golan v. Holder, 611 F.Supp.2d 1165, 90 U.S.P.Q.2d (BNA) 1202 (D. Colo. 2009) (full-text), citing Harper & Row Publishers, Inc. v. Nation Enters., 471 U.S. 539, 558 (1985) (full-text).
- Graham v. John Deere Co., 383 U.S. 1, 6 (1966) (full-text).
- Center for the Public Domain
- Center for the Study of the Public Domain
- Public Domain Review
- Public domain software