Introduction To Fair Use
There are two main categories of material that is not protected by copyright because they have fallen into the "public domain". The first category of material not protected by copyright is works that have fallen into the "public domain" because the copyright protection period has expired. The second category is those works prepared by the U.S. government, or government employees without the scope of their employment.
Expired Copyrights of Dead Authors
Most of the materials that have fallen into the public domain and thus are no longer protected by copyright, come from artists that have been dead a long time, such as Shakespeare.
As Shakespeare has been dead in excess of 100 years, any rights Shakespeare or his heirs had in and to his writings expired some time ago. This means that you may freely use Shakespeare's lines, characters, and stories in your own book, film, or screenplay. The same, however does not hold true for the writings of Robert Frost who died in 1963 because his writings are still copyright protected. The heirs of Robert Front presently own the copyrights in and to his writings and therefore are entitled to collect royalties from their performances or use.
U.S. copyright protection lasts for the life of the author (creator) plus 70 years. However, figuring out whether a work is in the public domain is not simply a matter of determining how long the author has been dead, since copyrights can last a lot longer than their creators. Unless you are certain that the copyright in a work has expired, you must investigate the copyright status of the work before reprinting it, adapting it, or otherwise exercising any of the other exclusive rights reserved to copyright owner(s).
U.S. Government Works
The second category of works that have no copyright protection are those works created by employees of the U.S. government as a part of their government jobs. However, before copying or adapting such a work you must make sure the work was in fact created by the U.S. Government, and not a semi-private government agency or contractor. Works created by the U.S. Government or employees of the U.S. Government are in the public domain because the government has chosen not to claim copyright in works created at the taxpayers' expense.
This means you may quote the entire text of a government publication without any special permission from the government. However, if your end creation consists predominantly of material produced by the government, your copyright notice should acknowledge the fact. For example:
"Copyright 2000 Melissa Marsh, except material reproduced on pages 10-20 and 40-50, which was taken from U.S. Government Publications "number", "title of publication'"
The only precaution necessary before using material from government publications is to make sure the material you want to use was prepared by the U.S. government proper and not by some private or semi-private agency of the government or a government contractor. You can probably do this by simply looking at the title page of the government publication or by calling the department or organization that published it. Anything published by the U.S. Government Printing Office or offered through the Consumer Information Catalog is almost certainly public domain material.
You can have the Copyright Office search its records for you to determine if a copyright is valid. The fee for this service is $65 per hour. Call the Reference and Bibliography Section of the Copyright Office at (202) 707-6850 for their estimate of the time required for your search. You must fill out a formal search request form and send it with the estimated search fee before the Copyright Office will begin your search.
A more expedient way to conduct a copyright search is to hire a professional search firm to examine the copyright records for you. Professional search firms charge larger fees for their services than the Copyright Office, but they should be able to get your search completed much more quickly.
It is also possible for you to personally search the files of the Copyright Office for registrations and related documents catalogued since January 1, 1978, via the Internet. Visit the Copyright Office at http://lcweb.loc.gov/copyright.