Overbreadth doctrine

In American jurisprudence, the overbreadth doctrine is primarily concerned with facial challenges to laws under the First Amendment. American courts have recognized several exceptions to the speech protected by the First Amendment (for example, obscenity, fighting words, and libel or defamation), and states therefore have some latitude to regulate unprotected speech. A statute doing so is overly broad (hence, overbreadth) if, in proscribing unprotected speech, it also proscribes protected speech. Because an overly broad law may deter constitutionally protected speech, the overbreadth doctrine allows a party to whom the law may constitutionally be applied to challenge the statute on the ground that it violates the First Amendment rights of others. See, e.g., Board of Trustees of State Univ. of N.Y. v. Fox, 492 U.S. 469, 483 (1989), and R. A. V. v. City of St. Paul, 505 U.S. 377 (1992). Overbreadth is closely related to vagueness; if a prohibition is expressed in a way that is too unclear for a person to reasonably know whether or not their conduct falls within the law, then to avoid the risk of legal consequences they often stay far away from anything that could possibly fit the uncertain wording of the law. The law's effects are thereby far broader than intended or than the U.S. Constitution permits, and hence the law is overbroad.