Works in the PUBLIC DOMAIN are free from all copyright restrictions. It matters because you can do anything you want with PUBLIC DOMAIN works: republish, quote, write a screen play, choreograph, direct, sing, play, screen, post . . . . (Of course you must always CITE the work.)
All US Government Documents are in the PUBLIC DOMAIN. (NOT all state government docs, however -- you have to check.)
Published works between 1923 and 1978 without copyright notices are in the PUBLIC DOMAIN.
Published works between 1923 and 1963 with copyright notices, but the copyrights were not renewed are in the PUBLIC DOMAIN. Stanford University is working on a searchable database of the copyright renewal records received by the US Copyright Office. This project will save you a lot of research hours. Less than 10% of the copyrights in this period were in fact renewed. http://collections.stanford.edu/copyrightrenewals/bin/page?forward=home
Published works between 1978 and 1 March 1989 without copyright notices and without subsequent registration are in the PUBLIC DOMAIN.
In addition, an author may voluntarily place a work into the PUBLIC DOMAIN at any time.
See indiviual topics on this site for more information, for example Screen a Film.
"Is it Protected by Copyright?" Michael Brewer, ALA Office for Information and Technology Policy http://librarycopyright.net/digitalslider/
“Yes, you can!” –Where you don’t even need ‘fair use’
Peter Jaszi, Washington College of Law, American University
When U.S. Works Pass into The Public Domain, Lolly Gasaway, UNC
Library Digitization Projects and Copyright, Mary Minow, J.D., A.M.L.S. http://www.llrx.com/features/digitization.htm
Who Owns Digital Works? by Ann Okerson http://www.library.yale.edu/%7Eokerson/sciam.html
Copyright Crash Course http://www.utsystem.edu/ogc/IntellectualProperty/cprtindx.htm
Two good links to links:
COPYRIGHT RESOURCES ONLINE http://www.library.yale.edu/%7Eokerson/copyproj.html
Copyright resources on the Web: Sites to keep you current, by David Hodgins http://www.ala.org/ala/acrl/acrlpubs/crlnews/backissues2007/march07/copyrightresources.htm
A useful book to check out:
Fishman, Stephen, The Public Domain, How to Find and Use Copyright-Free Writings, Music, Art & More, NOLO 2004. www.nolo.com
Diane Klare, Head of Reference, Olin Library,
firstname.lastname@example.org, ext. 3867 (for questions about this IP Web site, or copyright issues in general)
Library Reference Desk email@example.com, ext. 3873