The following is a reprint of the entire text of section 107 of Title 17, United States Code:
Section 107. Limitations on exclusive rights: Fair use
Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include:
(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use if such is made upon consideration of all the above factors.
Explanation of the Fair Use DoctrineBecause of the fair use doctrine, those who need access to certain works for the aforementioned accepted purposes can have it. Copyright is vital to authors and artists for the protection of their works, but fair use is vital to the public for access to those works. As long as copyright law remains, so must the fair use doctrine. Although the fair use doctrine makes it unnecessary to obtain permission to use small portions of copyrighted works, it is still proper to acknowledge the creator of the work that is used.
The law lists four factors to be evaluated in determining whether a particular use of a copyrighted work is a permitted "fair use," rather than an infringement of the copyright (above). Although all of these factors should be considered, the last factor is the most important in determining whether a particular use is "fair."
*From U.S. Code and excerpts by Lori L. Cressia (http://www.cas.usf.edu/english/walker/courses/fall97/fair.html)