In U.S. constitutional law, a facial challenge is a challenge to a statute in which the plaintiff alleges that the legislation is always unconstitutional, and therefore void. It is contrasted with an as-applied challenge, which alleges that a particular application of a statute is unconstitutional.
If a facial challenge is successful, a court will declare the statute in question facially invalid, which has the effect of striking it down entirely. This contrasts with a successful as-applied challenge, which will result in a court narrowing the circumstances in which the statute may constitutionally be applied without striking it down. In some cases—e.g., Gonzales v. Carhart or Crawford v. Marion County Election Board, a facial challenge has been rejected with either the court or concurring Justices intimating that the upheld statute might be vulnerable to an as-applied challenge.
In First Amendment cases, another type of facial challenge is enunciated in the overbreadth doctrine. If a statute reaches to include substantially protected conduct and speech in relation to the legitimate reach of the statute, then it is overbroad and thus void on its face.
As discussed above, one primary distinction between the two methods of challenging legislation in court is that a facial challenge to a statute seeks to invalidate it in its entirety because every application is unconstitutional, whereas an as-applied challenge seeks to invalidate a particular application of a statute. A second distinction between the two is that a facial challenge may be brought soon after a statute's passage in a legislature; however, an as-applied challenge, as the name suggests, can only be brought once it has been enforced. In this sense, a facial challenge is prospective, or forward looking, because it seeks to prevent a law from being enforced and thus violating someone's constitutional rights, and an as-applied challenge is retrospective, or backward looking, because it seeks to redress a constitutional violation that has already occurred. Since facial challenges have the potential to invalidate a statute in its entirety, they are said to be disfavored. Professor Richard Fallon of Harvard Law School has recently argued that both terms are ambiguous and not as easily distinguishable from one another. Indeed, the U.S. Supreme Court has recently acknowledged this fact. In Citizens United v. Federal Election Commission, it stated, "the distinction between facial and as-applied challenges is not so well defined that it has some automatic effect or that it must always control the pleadings and disposition in every case involving a constitutional challenge".