Censorship in the United States: The U.S. Congress enacts the Comstock Law, making it illegal to send any "obscene literature and articles of immoral use" through the mail.

In the United States, censorship involves the suppression of speech or public communication and raises issues of freedom of speech, which is protected by the First Amendment to the United States Constitution. Interpretation of this fundamental freedom has varied since its enshrinement. Traditionally, the First Amendment was regarded as applying only to the Federal government, leaving the states and local communities free to censor or not. As the applicability of states' rights in lawmaking vis-a-vis citizens' national rights began to wane in the wake of the Civil War, censorship by any level of government eventually came under scrutiny, but not without resistance. For example, in recent decades, censorial restraints increased during the 1950s period of widespread anti-communist sentiment, as exemplified by the hearings of the House Committee on Un-American Activities. In Miller v. California (1973), the U.S. Supreme Court found that the First Amendment's freedom of speech does not apply to obscenity, which can, therefore, be censored. While certain forms of hate speech are legal so long as they do not turn to action or incite others to commit illegal acts, more severe forms have led to people or groups being denied marching permits or the Westboro Baptist Church being sued, although the initial adverse ruling against the latter was later overturned on appeal to the U.S. Supreme Court case Snyder v. Phelps.

The Comstock Act of 1873 is a series of current provisions in federal law that generally criminalize the involvement of the United States Postal Service, its officers, or a common carrier in conveying obscene matter, crime-inciting matter, or certain abortion-related matter. The Comstock Act is largely codified across title 18 of the United States Code and was enacted beginning in 1872 with the attachment of a rider to the Post Office Consolidation Act of 1872. Amended multiple times since initial enactment, most recently in 1996, the Act is nonetheless often associated with U.S. Postal Inspector and anti-vice activist Anthony Comstock.