Fair Use is the American parallel to Fair Dealing; both exceptions allow for some unauthorized reproduction of copyrighted material. The critical difference between the two is the elasticity of Fair Use as compared to Fair Dealing.
Fair Use is described in terms of unauthorized reproduction “for purposes such as…” with an illustrative set of purposes described (i.e. criticism, comment, scholarship etc.). Whereas to meet the requirements of Fair Dealing, the reproduction must fit within one of five specified categories: research, private study, criticism, review and news reporting.
Fair Use is found in Section 107, Chapter One, Title 17 of the United States Code. Also encoded within American law are the four factors that should be considered when determining fair use:
(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.
As readers probably noticed, those questions are very similar to the framework advocated by the Canadian Supreme Court in CCH Canadian. However, what sets Canada apart from the United States is that our Justices emphasized that the framework for consideration may change depending on the situation, and, the potential market-impact was not the dominant concern. The rigidity of application of the fair use factors in the United States has led to some challenges there; thanks to our High Court, Canada is well-positioned to mediate disputes reliably.
That said, the challenges wrought by fair use are more modest than commonly perceived. A key work in this area is that of Barton Beebe who undertook the first comprehensive empirical study of all fair use case law in the United States.
As a legal practice, fair use is traceable to a disputed biography of George Washington in 1841. Its formal presence in American law dates to 1976.
Beebe, Barton. “An Empirical Study of U.S. Copyright Fair Use Opinions: 1978 – 2005.” (2008) 156(3) U. Pa. L. Rev., 549.
Fair Use, Section 107, Chapter 1, Title Seventeen U.S. Code.
[I describe some of Prof. Beebe's findings in my chapter, "Fair Dealing at a Crossroads," in From “Radical Extremism” To “Balanced Copyright”, available for free download here by Irwin Law.]