In American jurisprudence, the overbreadth doctrine is primarily concerned with facial challenges to laws under the First Amendment.
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 "strong medicine" of overbreadth invalidation need not and generally should not be administered when the statute under attack is unconstitutional as applied to the challenger before the court.
Specifically, the doctrine seeks to balance the "harmful effects" of "invalidating a law that in some of its applications is perfectly constitutional" as a possibility that "the threat of enforcement of an overbroad law deters people from engaging in constitutionally protected speech".
Similarly, "there must be a realistic danger that the statute itself will significantly compromise recognized First Amendment protections of parties not before the Court for it to be facially challenged on overbreadth grounds".
Citing Sargentich's note, the U.S. Supreme Court explicitly recognized the doctrine in 1973 in Broadrick v. Oklahoma, where the Court stated "the possible harm to society in permitting some unprotected speech to go unpunished is outweighed by the possibility that protected speech of others may be muted and perceived grievances left to fester because of the possible inhibitory effects of overly broad statutes".