Roberts, C. J., delivered the opinion of the Court, in which Stevens, Scalia, Kennedy, Thomas, Ginsburg, Breyer, and Sotomayor, JJ., joined. Alito, J., filed a dissenting opinion.

     Congress enacted 18 U. S. C. §48 to criminalize the commercial creation, sale, or possession of certain depictions of animal cruelty. The statute does not address underlying acts harmful to animals, but only portrayals of such conduct. The question presented is whether the prohibition in the statute is consistent with the freedom of speech guaranteed by the First Amendment.

I

     Section 48 establishes a criminal penalty of up to five years in prison for anyone who knowingly "creates, sells, or possesses a depiction of animal cruelty," if done "for commercial gain" in interstate or foreign commerce. §48(a).  A depiction of "animal cruelty" is defined as one "in which a living animal is intentionally maimed, mutilated, tortured, wounded, or killed," if that conduct violates federal or state law where "the creation, sale, or possession takes place." In what is referred to as the "exceptions clause," the law exempts from prohibition any depiction "that has serious religious, political, scientific, educational, journalistic, historical, or artistic value."

     The legislative background of §48 focused primarily on the interstate market for "crush videos." According to the House Committee Report on the bill, such videos feature the intentional torture and killing of helpless animals, including cats, dogs, monkeys, mice, and hamsters. Crush videos often depict women slowly crushing animals to death "with their bare feet or while wearing high heeled shoes," sometimes while "talking to the animals in a kind of dominatrix patter" over "[t]he cries and squeals of the animals, obviously in great pain." Apparently these depictions "appeal to persons with a very specific sexual fetish who find them sexually arousing or otherwise exciting." The acts depicted in crush videos are typically prohibited by the animal cruelty laws enacted by all 50 States and the District of Columbia. But crush videos rarely disclose the participants' identities, inhibiting prosecution of the underlying conduct.

     This case, however, involves an application of §48 to depictions of animal fighting. Dogfighting, for example, is unlawful in all 50 States and the District of Columbia, and has been restricted by federal law since 1976. Respondent Robert J. Stevens ran a business, "Dogs of Velvet and Steel," and an associated Web site, through which he sold videos of pit bulls engaging in dogfights and attacking other animals. Among these videos were Japan Pit Fights and Pick-A-Winna: A Pit Bull Documentary, which include contemporary footage of dogfights in Japan (where such conduct is allegedly legal) as well as footage of American dogfights from the 1960's and 1970's.² A third video, Catch Dogs and Country Living, depicts the use of pit bulls to hunt wild boar, as well as a "gruesome" scene of a pit bull attacking a domestic farm pig. On the basis of these videos, Stevens was indicted on three counts of violating §48.

     Stevens moved to dismiss the indictment, arguing that §48 is facially invalid under the First Amendment. The District Court denied the motion. It held that the depictions subject to §48, like obscenity or child pornography, are categorically unprotected by the First Amendment. It went on to hold that §48 is not substantially overbroad, because the exceptions clause sufficiently narrows the statute to constitutional applications. The jury convicted Stevens on all counts, and the District Court sentenced him to three concurrent sentences of 37 months' imprisonment, followed by three years of supervised release....

     We granted certiorari.

II

     The Government's primary submission is that §48 necessarily complies with the Constitution because the banned depictions of animal cruelty, as a class, are
categorically unprotected by the First Amendment. We disagree.

     The First Amendment provides that "Congress shall make no law ... abridging the freedom of speech." "[A]s a general matter, the First Amendment means that government has no power to restrict expression because of its message, its ideas, its subject matter, or its content." Section 48 explicitly regulates expression based on content: The statute restricts "visual [and] auditory depiction[s]," such as photographs, videos, or sound recordings, depending on whether they depict conduct in which a living animal is intentionally harmed. As such, §48 is " 'presumptively invalid,' and the Government bears the burden to rebut that presumption." 

     "From 1791 to the present," however, the First Amendment has "permitted restrictions upon the content of speech in a few limited areas," and has never "include[d] a freedom to disregard these traditional limitations." These "historic and traditional categories long familiar to the bar,"--including obscenity, defamation, fraud, incitement, and speech integral to criminal conduct, Giboney v. Empire Storage & Ice Co., 336 U. S. 490, 498 (1949)--are "well-defined and narrowly limited classes of speech, the prevention and punishment of which have never been thought to raise any Constitutional problem." 

     The Government argues that "depictions of animal cruelty" should be added to the list. It contends that depictions of "illegal acts of animal cruelty" that are "made, sold, or possessed for commercial gain" necessarily "lack expressive value," and may accordingly "be regulated as unprotected speech." The claim is not just that Congress may regulate depictions of animal cruelty subject to the First Amendment, but that these depictions are outside the reach of that Amendment altogether--that they fall into a " 'First Amendment Free Zone.' " 

     ....The Government thus proposes that a claim of categorical exclusion should be considered under a simple balancing test: "Whether a given category of speech enjoys First Amendment protection depends upon a categorical balancing of the value of the speech against its societal costs." As a free-floating test for First Amendment coverage, that sentence is startling and dangerous. The First Amendment's guarantee of free speech does not extend only to categories of speech that survive an ad hoc balancing of relative social costs and benefits. The First Amendment itself reflects a judgment by the American people that the benefits of its restrictions on the Government outweigh the costs. Our Constitution forecloses any attempt to revise that judgment simply on the basis that some speech is not worth it. The Constitution is not a document "prescribing limits, and declaring that those limits may be passed at pleasure." 

     To be fair to the Government, its view did not emerge from a vacuum. As the Government correctly notes, this Court has often described historically unprotected categories of speech as being " 'of such slight social value as a step to truth that any benefit that may be derived from them is clearly outweighed by the social interest in order and morality.' " We noted that within these categories of unprotected speech, "the evil to be restricted so overwhelmingly outweighs the expressive interests, if any, at stake, that no process of case-by-case adjudication is required," because "the balance of competing interests is clearly struck." The Government derives its proposed test from these descriptions in our precedents.

     But such descriptions are just that--descriptive. They do not set forth a test that may be applied as a general matter to permit the Government to imprison any speaker so long as his speech is deemed valueless or unnecessary, or so long as an ad hoc calculus of costs and benefits tilts in a statute's favor.

     When we have identified categories of speech as fully outside the protection of the First Amendment, it has not been on the basis of a simple cost-benefit analysis. In Ferber, for example, we classified child pornography as such a category. We noted that the State of New York had a compelling interest in protecting children from abuse, and that the value of using children in these works (as opposed to simulated conduct or adult actors) was de minimis. But our decision did not rest on this "balance of competing interests" alone. We made clear that Ferber presented a special case: The market for child pornography was "intrinsically related" to the underlying abuse, and was therefore "an integral part of the production of such materials, an activity illegal throughout the Nation." As we noted, " '[i]t rarely has been suggested that the constitutional freedom for speech and press extends its immunity to speech or writing used as an integral part of conduct in violation of a valid criminal statute.' " Ferber thus grounded its analysis in a previously recognized, long-established category of unprotected speech, and our subsequent decisions have shared this understanding.

     Our decisions in Ferber and other cases cannot be taken as establishing a freewheeling authority to declare new categories of speech outside the scope of the First Amendment. Maybe there are some categories of speech that have been historically unprotected, but have not yet been specifically identified or discussed as such in our case law. But if so, there is no evidence that "depictions of animal cruelty" is among them. We need not foreclose the future recognition of such additional categories to reject the Government's highly manipulable balancing test as a means of identifying them.

III

     Because we decline to carve out from the First Amendment any novel exception for §48, we review Stevens's First Amendment challenge under our existing doctrine.

A

     Stevens challenged §48 on its face, arguing that any conviction secured under the statute would be unconstitutional.  To succeed in a typical facial attack, Stevens would have to establish "that no set of circumstances exists under which [§48] would be valid" or that the statute lacks any "plainly legitimate sweep."  Here the Government asserts that Stevens cannot prevail because §48 is plainly legitimate as applied to crush videos and animal fighting depictions. Deciding this case through a traditional facial analysis would require us to resolve whether these applications of §48 are in fact consistent with the Constitution.

     In the First Amendment context, however, this Court recognizes "a second type of facial challenge," whereby a law may be invalidated as overbroad if "a substantial number of its applications are unconstitutional, judged in relation to the statute's plainly legitimate sweep." Stevens argues that §48 applies to common depictions of ordinary and lawful activities, and that these depictions constitute the vast majority of materials subject to the statute. The Government makes no effort to defend such a broad ban as constitutional. Instead, the Government's entire defense of §48 rests on interpreting the statute as narrowly limited to specific types of "extreme" material. As the parties have presented the issue, therefore, the constitutionality of §48 hinges on how broadly it is construed. It is to that question that we now turn.

B

     The first step in overbreadth analysis is to construe the challenged statute; it is impossible to determine whether a statute reaches too far without first knowing what the statute covers...We read §48 to create a criminal prohibition of alarming breadth. To begin with, the text of the statute's ban on a "depiction of animal cruelty" nowhere requires that the depicted conduct be cruel. That text applies to "any ... depiction" in which "a living animal is intentionally maimed, mutilated, tortured, wounded, or killed." "[M]aimed, mutilated, [and] tortured" convey cruelty, but "wounded" or "killed" do not suggest any such limitation.

     The Government contends that the terms in the definition should be read to require the additional element of "accompanying acts of cruelty." The Government bases this argument on the definiendum, "depiction of animal cruelty" and on " 'the commonsense canon of noscitur a sociis.' " As that canon recognizes, an ambiguous term may be "given more precise content by the neighboring words with which it is associated." Likewise, an unclear definitional phrase may take meaning from the term to be defined.

     But the phrase "wounded ... or killed" at issue here contains little ambiguity. The Government's opening brief properly applies the ordinary meaning of these words, stating for example that to " 'kill' is 'to deprive of life.' " We agree that "wounded" and "killed" should be read according to their ordinary meaning. Nothing about that meaning requires cruelty.

     While not requiring cruelty, §48 does require that the depicted conduct be "illegal." But this requirement does not limit §48 along the lines the Government suggests. There are myriad federal and state laws concerning the proper treatment of animals, but many of them are not designed to guard against animal cruelty. Protections of endangered species, for example, restrict even the humane "wound[ing] or kill[ing]" of "living animal[s]." Livestock regulations are often designed to protect the health of human beings, and hunting and fishing rules (seasons, licensure, bag limits, weight requirements) can be designed to raise revenue, preserve animal populations, or prevent accidents. The text of §48(c) draws no distinction based on the reason the intentional killing of an animal is made illegal, and includes, for example, the humane slaughter of a stolen cow.

     What is more, the application of §48 to depictions of illegal conduct extends to conduct that is illegal in only a single jurisdiction. Under subsection (c)(1), the depicted conduct need only be illegal in "the State in which the creation, sale, or possession takes place, regardless of whether the ... wounding ... or killing took place in [that] State." A depiction of entirely lawful conduct runs afoul of the ban if that depiction later finds its way into another State where the same conduct is unlawful. This provision greatly expands the scope of §48, because although there may be "a broad societal consensus" against cruelty to animals, there is substantial disagreement on what types of conduct are properly regarded as cruel. Both views about cruelty to animals and regulations having no connection to cruelty vary widely from place to place.

     In the District of Columbia, for example, all hunting is unlawful. Other jurisdictions permit or encourage hunting, and there is an enormous national market for hunting-related depictions in which a living animal is intentionally killed.... Nonetheless, because the statute allows each jurisdiction to export its laws to the rest of the country, §48(a) extends to any magazine or video depicting lawful hunting, so long as that depiction is sold within the Nation's Capital....

      The disagreements among the States--and the "commonwealth[s], territor[ies], or possession[s] of the United States"--extend well beyond hunting. State agricultural regulations permit different methods of livestock slaughter in different places or as applied to different animals. California has recently banned cutting or "docking" the tails of dairy cattle, which other States permit. Even cockfighting, long considered immoral in much of America, is legal in Puerto Rico and was legal in Louisiana until 2008. An otherwise-lawful image of any of these practices, if sold or possessed for commercial gain within a State that happens to forbid the practice, falls within the prohibition of §48(a).

C

     The only thing standing between defendants who sell such depictions and five years in federal prison--other than the mercy of a prosecutor--is the statute's exceptions clause. Subsection (b) exempts from prohibition "any depiction that has serious religious, political, scientific, educational, journalistic, historical, or artistic value." The Government argues that this clause substantially narrows the statute's reach: News reports about animal cruelty have "journalistic" value; pictures of bullfights in Spain have "historical" value; and instructional hunting videos have "educational" value. Thus, the Government argues, §48 reaches only crush videos, depictions of animal fighting, and perhaps other depictions of "extreme acts of animal cruelty." 

     The Government's attempt to narrow the statutory ban, however, requires an unrealistically broad reading of the exceptions clause...We decline the Government's invitation--advanced for the first time in this Court--to regard as "serious" anything that is not "scant."

D

     Not to worry, the Government says: The Executive Branch construes §48 to reach only "extreme" cruelty, Brief for United States 8, and it "neither has brought nor will bring a prosecution for anything less.' The Government hits this theme hard, invoking its prosecutorial discretion several times. But the First Amendment protects against the Government; it does not leave us at the mercy of noblesse oblige. We would not uphold an unconstitutional statute merely because the Government promised to use it responsibly....

*  *  *

     Justice Alito, dissenting.

     The Court strikes down in its entirety a valuable statute that was enacted not to suppress speech, but to prevent horrific acts of animal cruelty--in particular, the creation and commercial exploitation of "crush videos," a form of depraved entertainment that has no social value....

     Instead of applying the doctrine of overbreadth, I would vacate the decision below and instruct the Court of Appeals on remand to decide whether the videos that respondent sold are constitutionally protected. If the question of overbreadth is to be decided, however, I do not think the present record supports the Court's conclusion that §48 bans a substantial quantity of protected speech....