Although speech is freer in the United States than in many societies, federal and state laws do restrict many kinds of expression. Some kinds of speech regarded as damaging to individual interests (e.g., libel and slander) are limited primarily by the threat of tort action; other forms of speech (e.g., obscenity) are restricted by law because they are regarded as damaging to society as a whole. Speech that is regarded as disruptive of public order has long been beyond protection (e.g., "fighting words" that cause a breach of the peace or false statements that cause general panic). The government also limits speech that threatens it directly; although sedition laws are rarely prosecuted in the United States, such rationales as a danger to "national security" have been invoked to silence criticism of or opposition to the government. Laws designed to silence opposition to organized religion (e.g., laws against blasphemy or heresy), common in some other countries, would run afoul of the First Amendment.
In recent decades speech controversies in the United States have involved, among other issues, whether and how "hate speech" directed at racial or other groups can be suppressed and what limitations may be imposed on speech in an attempt to combat sexual harassment. The definition of speech itself has been broadened to encompass "symbolic speech," which consists of actions that express opinions; thus, U.S. courts have held that burning the American flag as a protest is protected speech.
See G. R. Stone, Perilous Times: Free Speech in Wartime from the Sedition Act of 1798 to the War on Terrorism (2004).