The fair use doctrine is an aspect of United States copyright law that provides for the licit, non-licensed citation or incorporation of copyrighted material in another author's work under certain, specifiable conditions. The term "fair use" is unique to the United States; a similar principle, fair dealing, exists in some other common law jurisdictions.
Fair use makes copyrighted work available to the public as raw material without the need for permission or clearance, so long as such free usage serves the purpose of copyright law, which the U.S. Constitution defines as the promotion of "the Progress of Science and useful Arts" (I.1.8), better than the legal enforcement of claims of infringement. The doctrine hereby attempts to balance the interests of individual copyright holders with the social or cultural benefits that follow from the creation and distribution of derivative works. Insofar as this doctrine protects forms of expression that might otherwise be enjoined as copyright infringing, it has been related to First Amendment free speech protections in the U.S. Constitution.
Fair use under United States law
The legal concept of "copyright" was first ratified by Britain's Statute of Anne of 1709. As room was not made for the unauthorized reproduction of copyrighted content within this newly formulated statutory right, the courts gradually created a doctrine of "fair abridgement", which later became "fair use", that recognized the utility of such actions. The doctrine only existed in the U.S. as common law until it was incorporated into the Copyright Act of 1976, 17 U.S.C. § 107 (
http://caselaw.lp.findlaw.com/scripts/ts_search.pl?title=17&sec=107), excerpted here:
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.
More:
http://en.wikipedia.org/wiki/Fair_use