U.S. Code, Title 17, Chapter One, 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The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
Fair Use
It can be difficult to determine whether or not your use of a copyrighted item falls within fair use guidelines. Here are some resources to help you determine whether or not your use is fair use.
Fair Use Checklist (Kenneth D. Crews and Dwayne K. Butler)
This Fair Use Checklist can help you decide if your use favors or opposes fair use considering the four factors above.
The Fair Use Index is searchable by jurisdiction or category (of copyrighted material), or can be viewed chronologically.