The right to free speech is a long-standing tradition in the United States, but actually respecting the right to free speech is not. According to the American Civil Liberties Union (ACLU), censorship is "the suppression of words, images or ideas that are "offensive," and it happens "whenever some people succeed in imposing their personal political or moral values on others." Our freedom of expression may be limited, says the ACLU, "only if it will clearly cause direct and imminent harm to an important societal interest." This history of censorship in America describes the major steps to restrict speech taken by individuals, groups, and the government since the founding of the country, as well as the outcomes of battles to overturn them.

1798: John Adams Gets Revenge on His Critics Keith Lance / Getty Images "Old, querulous, bald, blind, crippled, toothless Adams," one supporter of challenger Thomas Jefferson called the incumbent president. But Adams got the last laugh, signing a bill in 1798 that made it illegal to criticize a government official without backing up one's criticisms in court. Twenty-five people were arrested under the law, though Jefferson pardoned its victims after he defeated Adams in the 1800 election. Later sedition acts focused primarily on punishing those who advocated civil disobedience. The Sedition Act of 1918, for example, targeted draft resisters.

1821: The Longest Ban in US History Ronald Dumont / Getty Images The bawdy novel ​"Fanny Hill" (1748), written by John Cleland as an exercise in what he imagined a prostitute's memoirs might sound like, was no doubt familiar to the Founding Fathers; we know that Benjamin Franklin, who himself wrote some fairly risque material, had a copy. But later generations were less latitudinarian. The book holds the record for being banned longer than any other literary work in the United States--prohibited in 1821, and not legally published until the Supreme Court overturned the ban in Memoirs v. Massachusetts (1966). Of course, once it was legal it lost much of its appeal: by 1966 standards, nothing written in 1748 was liable to shock anybody.

1873: Anthony Comstock, Mad Censor of New York Bettmann / Getty Images If you're looking for a clear-cut villain in the history of U.S. censorship, you've found him. In 1872, feminist Victoria Woodhull published an account of an affair between a celebrity evangelical minister and one of his parishioners. Comstock, who despised feminists, requested a copy of the book under a fake name, then reported Woodhull and had her arrested on obscenity charges. He soon became head of the New York Society for the Suppression of Vice, where he successfully campaigned for an 1873 federal obscenity law, commonly referred to as the Comstock Act, that allowed warrantless searches of the mail for "obscene" materials. Comstock later boasted that during his career as censor, his work led to the suicides of 15 alleged "smut-peddlers."

1921: The Strange Odyssey of Joyce's Ulysses Ingolf Pompe / LOOK-foto / Getty Images The New York Society for the Suppression of Vice successfully blocked the publication of Irish writer James Joyce's "Ulysses" in 1921, citing a relatively tame masturbation scene as proof of obscenity. U.S. publication was finally permitted in 1933 following the US District Court ruling United States v. One Book Called Ulysses, in which Judge John Woolsey found that the book was not obscene and essentially established artistic merit as an affirmative defense against obscenity charges.

1930: The Hays Code Takes on Movie Gangsters, Adulterers Breen (center) was an administrator of the Production Code, the American censorship body, governed by the 'Hays Office.'. Kurt Hutton / Getty Images The Hays Code was never enforced by the government—it was voluntarily agreed upon by film distributors—but the threat of government censorship made it necessary. The U.S. Supreme Court had already ruled in Mutual Film Corporation v. Industrial Commission of Ohio (1915) that movies were not protected by the First Amendment, and some foreign films had been seized on obscenity charges. The film industry adopted the Hays Code as a means of avoiding outright federal censorship. The Hays Code, which regulated the industry from 1930 until 1968, banned what you might expect it to ban—violence, sex, and profanity—but it also prohibited portrayals of interracial or same-sex relationships, as well as any content that was deemed anti-religious or anti-Christian. Roth v. U.S. was a 1957 case that confirmed that obscenity, which appealed to prurient interests, was not constitutionally protected.

1954: Making Comic Books Kid-Friendly (and Bland) crisserbug / Getty Images Like the Hays Code, the Comics Code Authority (CCA) is a voluntary industry standard. Because comics are still primarily read by children—and because it has historically been less binding on retailers than the Hays Code was on distributors—the CCA is less dangerous than its film counterpart. This may be why it is still in use today, though most comic book publishers ignore it and no longer submit material for CCA approval. The driving force behind the CCA was the fear that violent, dirty or otherwise questionable comics might turn children into juvenile delinquents—which was the central thesis of Frederic Wertham's 1954 bestseller "Seduction of the Innocent" (which also argued, less credibly, that the Batman-Robin relationship might turn children gay).

1959: Lady Chatterley's Moratorium Derek Berwin / Getty Images Although Senator Reed Smoot admitted that he had not read D.H. Lawrence's "Lady Chatterley's Lover" (1928), he expressed strong opinions about the book. "It is most damnable!" he complained in a 1930 speech. "It is written by a man with a diseased mind and a soul so black that he would obscure even the darkness of hell!" Lawrence's odd story about an adulterous affair between Constance Chatterley and her husband's servant was so offensive because, at the time, non-tragic portrayals of adultery were, for practical purposes, nonexistent. The Hays Code banned them from films, and federal censors banned them from print media. A 1959 federal obscenity trial lifted the ban on the book, now recognized as a classic.

1971: The New York Times Takes on the Pentagon and Wins Robert Daemmrich Photography Inc / Getty Images The massive military study titled "United States–Vietnam Relations, 1945–1967: A Study Prepared by the Department of Defense," later known as the Pentagon Papers was supposed to be classified. But when excerpts of the document were leaked to The New York Times in 1971, which published them, all hell broke loose—with President Richard Nixon threatening to have journalists indicted for treason, and federal prosecutors attempting to block further publication. (They had reason to do so. The documents revealed that U.S. leaders had—among other things--specifically taken measures to prolong and escalate the unpopular war.) In June 1971, the Supreme Court ruled 6–3 that the Times could legally publish the Pentagon Papers.

1973: Obscenity Defined Barbara Alper / Getty Images A 5–4 majority of the Supreme Court, led by Chief Justice Warren Burger, outlined the current definition of obscenity in Miller v. California (1973), a mail-order porn case, as follows: the average person must find that the work, taken as a whole, appeals to the prurient interest;

the work depicts or describes, in a patently offensive way, sexual conduct or excretory functions specifically defined by applicable state law; and

the work, taken as a whole, lacks serious literary, artistic, political or scientific value. While the Supreme Court has held since 1897 that the First Amendment does not protect obscenity, the relatively small number of obscenity prosecutions in recent years suggests otherwise.

1978: The Indecency Standard Paul Natkin / Getty Images When George Carlin's "Seven Dirty Words" routine was aired on a New York radio station in 1973, a father listening to the station complained to the Federal Communications Commission (FCC). The FCC, in turn, wrote the station a firm letter of reprimand. The station challenged the reprimand, ultimately leading to the Supreme Court's landmark FCC v. Pacifica (1978) in which the Court held that material that is "indecent," but not necessarily obscene, may be regulated by the FCC if it is distributed through publicly owned wavelengths. Indecency, as defined by the FCC, refers to "language or material that, in context, depicts or describes, in terms patently offensive as measured by contemporary community standards for the broadcast medium, sexual or excretory organs or activities."

1996: The Communications Decency Act of 1996 designer491 / Getty Images The Communications Decency Act of 1996 mandated a federal prison sentence of up to two years for anyone who knowingly "uses any interactive computer service to display in a manner available to a person under 18 years of age, any comment, request, suggestion, proposal, image or other communication that, in context, depicts or describes, in terms patently offensive as measured by contemporary community standards, sexual or excretory activities or organs." The Supreme Court mercifully struck the act down in ACLU v. Reno (1997), but the concept of the bill was revived with the Child Online Protection Act (COPA) of 1998, which criminalized any content deemed "harmful to minors." Courts immediately blocked COPA, which was formally struck down in 2009.

2004: The FCC Meltdown KMazur / Getty Images During the live broadcast of the Super Bowl halftime show on February 1, 2004, Janet Jackson's right breast was slightly exposed; the FCC responded to an organized campaign by enforcing indecency standards more aggressively than it ever had before. Soon every expletive uttered at an awards show, every bit of nudity (even pixelated nudity) on reality television and every other potentially offensive act became a possible target of FCC scrutiny.