United States defamation law

The origins of the United States' defamation laws pre-date the American Revolution; one influential case in 1734 involved John Peter Zenger and established precedent that "The Truth" is an absolute defense against charges of libel. Though the First Amendment of the U.S. Constitution was designed to protect freedom of the press, for most of the history of the United States, the U.S. Supreme Court failed to use it to rule on libel cases. This left libel laws, based upon the traditional "Common Law" of defamation inherited from the English legal system, mixed across the states. The 1964 case New York Times Co. v. Sullivan, however, radically changed the nature of libel law in the United States by establishing that public officials could win a suit for libel only when they could prove the media outlet in question knew either that the information was wholly and patently false or that it was published "with reckless disregard of whether it was false or not". Later Supreme Court cases barred strict liability for libel and forbade libel claims for statements that are so ridiculous as to be obviously facetious. Recent cases have added precedent on defamation law and the Internet.

The First Amendment's guarantees of freedom of speech and freedom of the press provide defendants in the United States a measure of protection from defamation lawsuits. Some variation exists among the several states as to the extent to which the states' legislatures have passed statutes or their courts have handed down decisions affecting the contours inherited from common law. Some states codify what constitutes slander and libel together into the same set of laws.

Criminal libel is rarely prosecuted but exists on the books in many states, and is constitutionally permitted in circumstances essentially identical to those where civil libel liability is constitutional. Defenses to libel that can result in dismissal before trial include the statement being one of opinion rather than fact or being "fair comment and criticism", though neither of these are imperatives on the US constitution. Truth is an absolute defense against defamation in the United States,^[1] meaning true statements cannot be defamatory.^[2]

Most states recognize that some categories of false statements are considered to be defamatory per se, such that people making a defamation claim for these statements do not need to prove that the statement caused them actual damages. (See section Defamation per se.)