Fair use is a doctrine in United States law that permits limited use of copyrighted material without having to first acquire permission from the copyright holder. Fair use is one of the limitations to copyright intended to balance the interests of copyright holders with the public interest in the wider distribution and use of creative works by allowing as a defense to copyright infringement claims certain limited uses that might otherwise be considered infringement. The U.S. "fair use doctrine" is generally broader than the "fair dealing" rights known in most countries that inherited English Common Law. The fair use right is a general exception that applies to all different kinds of uses with all types of works. In the U.S., fair use right/exception is based on a flexible proportionality test that examines the purpose of the use, the nature of the copyrighted work, the amount used, and the impact on the market of the original work.

The doctrine of "fair use" originated as a judicially-created common law during the 18th and 19th centuries as a way of preventing copyright law from being too rigidly applied and "stifling the very creativity which [copyright] law is designed to foster." Though originally a common law doctrine, it was enshrined in statutory law when the U.S. Congress passed the Copyright Act of 1976. The U.S. Supreme Court has issued several major decisions clarifying and reaffirming the fair use doctrine since the 1980s, the most recent being in the 2023 decision Andy Warhol Foundation for the Visual Arts, Inc. v. Goldsmith.

The 1710 Statute of Anne, an act of the Parliament of Great Britain, created copyright law to replace a system of private ordering enforced by the Stationers' Company. The Statute of Anne did not provide for legal unauthorized use of material protected by copyright. In Gyles v Wilcox, the Court of Chancery established the doctrine of "fair abridgement", which permitted unauthorized abridgement of copyrighted works under certain circumstances. Over time, this doctrine evolved into the modern concepts of fair use and fair dealing. Fair use was a common-law (i.e. created by judges as a legal precedent) doctrine in the U.S. until it was incorporated into the Copyright Act of 1976, 17 U.S.C. § 107.

The term "fair use" originated in the United States. Although related, the limitations and exceptions to copyright for teaching and library archiving in the U.S. are located in a different section of the statute. A similar-sounding principle, fair dealing, exists in some other common law jurisdictions but in fact it is more similar in principle to the enumerated exceptions found under civil law systems. Civil law jurisdictions have other limitations and exceptions to copyright.

In response to perceived over-expansion of copyrights, several electronic civil liberties and free expression organizations began in the 1990s to add fair use cases to their dockets and concerns. These include the Electronic Frontier Foundation ("EFF"), the American Civil Liberties Union, the National Coalition Against Censorship, the American Library Association, numerous clinical programs at law schools, and others. The "Chilling Effects" archive was established in 2002 as a coalition of several law school clinics and the EFF to document the use of cease and desist letters. In 2006 Stanford University began an initiative called the "Fair Use Project" (FUP) to help artists, particularly filmmakers, fight lawsuits brought against them by large corporations.

Examples of fair use in United States copyright law include commentary, search engines, criticism, parody, news reporting, research, and scholarship. Fair use provides for the legal, unlicensed citation or incorporation of copyrighted material in another author's work under a four-factor test.

The U.S. Supreme Court has traditionally characterized fair use as an affirmative defense, but in Lenz v. Universal Music Corp. (2015) (the "dancing baby" case), the U.S. Court of Appeals for the Ninth Circuit concluded that fair use was not merely a defense to an infringement claim, but was an expressly authorized right, and an exception to the exclusive rights granted to the author of a creative work by copyright law: "Fair use is therefore distinct from affirmative defenses where a use infringes a copyright, but there is no liability due to a valid excuse, e.g., misuse of a copyright."

17 U.S.C. § 107