Pornography is the representation of the human body or human sexual behaviour with the goal of sexual arousal, similar to erotica. Pornography may use any of a variety of media and sounds such as heavy breathing. Pornographic films combine moving images, spoken erotic text or other erotic sounds, while magazines often combine photos and written text. Novels and short stories provide written text, sometimes with illustrations. In addition to media, a live performance may also be called pornographic. Pornography has an extensive history. Sexual artwork is among the oldest known to exist, and explicit photographs date to the beginning of photography and among the earliest films are works depicting nudity and explicit sex.

Nude human beings and sexual activities are depicted in some paleolithic art, such as Venus Figurines. However, it is not certain that the purpose was sexual arousal, as the images may have had instead a spiritual significance. There are numerous pornographic paintings on the walls of ruined Roman buildings in Pompeii. One notable example is a brothel in which the various sexual services are advertised in murals above each door. In Pompeii you can also see phalli and testicles engraved in the sidewalks, pointing the way to the prostitution and entertainment district, to aid visitors in finding their way. Archaeologists in Germany reported that they had found what they believe is a 7,200-year-old pornographic scene depicting a male figurine bending over a female figurine in a manner suggestive of sexual intercourse. The male figure has been named Adonis von Zschernitz.

A lot of pornography is digitally manipulated in sophisticated image editors such as Adobe Photoshop. This practice ranges from applying mild changes to photographs to improve the appearance of the models, such as removing skin defects, improving brightness and contrast of the photo, to extensive editing to produce images of non-existent creatures such as catgirls, or celebrities who may not have themselves ever consented to be filmed for pornography. Digital manipulation requires the use of source photographs, but some pornography is produced without human actors at all. The idea of completely computer-generated pornography was conceived very early as one of the most obvious areas of application for computer graphics and 3D rendering. However, until the late 1990s it could not be produced cost-effectively. In early 2000s it became a growing segment, as the modeling and animation software matured and rendering capabilities of computers improved. The strongest advantage of computer-generated pornography is the ability to realistically render sexual fantasies that are impossible or illegal to film in reality. As of 2004, computer-generated pornography depicting situations involving children and sex with fictional characters such as Lara Croft is already produced on a limited scale. The October 2004 issue of Playboy featured topless pictures of the title character from the BloodRayne videogame. With the arrival of the Internet, the availability of pornography increased greatly. Many of the most successful internet entrepreneurs are those who operate pornographic internet sites, and the porn industry is usually credited as being the first to make money off the internet. As well as conventional photographic or video pornography, some sites offer interactive video game-like entertainment. Due to the international character of the Internet, it provides an easy means for consumers of pornography that is illegal in their country to simply acquire such material from sources in another country where it is legal or not prosecuted. The almost-zero cost of copying and shipping of digital data boosted the formation of private circles of people swapping pornography. This type of exchange is especially popular for material that is illegal, most notably child pornography and bestiality. With the advent of peer to peer file sharing applications such as Kazaa, pornography swapping has reached new heights. Free pornography became available en masse from other users and is no longer restricted to private groups. Cheap digital cameras, increasingly powerful and userfriendly software, and easy access to pornographic source material have made it possible for individuals to produce and share house-made or house-altered porn for next to no cost. This is most notable in the evolution of 3D rendered porn and the enhancement of existing material by blending celebrities into them. On the Internet, pornography is often referred to as pr0n which is misspelled p0rn, porn written with zero, a common style in a so called leet speak. One theory on the origins of this spelling is that it was devised to fool spam filters which blocked emails with the word "porn" from coming through to the recipient. However, since leet speak has performed similar mutations on a number of words, including those unlikely to feature in unsolicited commercial e-mails, it is likely that any transformation of "porn" to "pr0n" for spamming purposes is at best an independent invention.

In the second half of the 20th century, pornography in the United States evolved from the so-called men's magazines such as Playboy and Modern Man of the 1950s. These magazines featured nude or semi-nude women, sometimes apparently engaging in the act of masturbation, although their genitals or pubic hair were not actually displayed. By the late 1960s, however, these magazines, which now included Penthouse, began to evolve into more explicit displays, eventually, by the 1990s, featuring sexual penetration, lesbianism and homosexuality, group sex, and fetishes. The first explicitly pornographic film with a plot that received a general theatrical release in the U.S. is generally considered to be Mona (Mona the Virgin Nymph), a 1970 feature by Bill Osco and Howard Ziehm, who went on to create the relatively high-budget cult film Flesh Gordon. The 1971 film The Boys in the Sand represented a number of pornographic firsts. It was the first generally available gay pornographic movie, the first porn film to include onscreen credits for its cast and crew, and the first porn film to parody the title of a mainstream movie. And it is the only X-rated pornographic film to be reviewed by The New York Times.

Criticisms of pornography come from three directions: conservatism, religion, and feminism. Religious conservatives decry pornography because they see it as immoral. According to them, sex is reserved for married couples, and pornography is thought to lead to an overall increase in what they consider to be immoral behavior in society. Lust caused or directed through pornography may be interpreted as an indication of dissatisfaction with a spouse and is demurred by many religious teachings. Feminist critics generally criticize pornography as degrading to its subjects, and an example of a male-centered objectification of women. Critics from both groups have sometimes expressed belief in the existence of pornography addiction. While almost any human behavior can be taken to the level of an addiction and there are several popular 12-step programs for people who believe they may have this or other sexually related addiction problems. Many charge that the concept of "pornography addiction" is frequently raised not because it is scientifically sound but because it creates links between pornography and deviant behavior in the public mind.

Pornography has been a driving force behind the adoption of many technologies. Mass-distributed pornography is as old as the printing press. Almost as soon as photography was invented, it was being used to produce pornographic photographs. The movie camera has also been used for pornography throughout its history, and with the arrival of the home video cassette recorder the pornographic movie industry grew massively, people being able not only to view pornography in the privacy of their own home without having to go out to a theater, but also to make their own pornography. The fact that the adult industry has such a large consumer base has been used to suggest that it can affect even the development of technology. An oft-cited example is the suggestion that Sony Betamax lost the format war to VHS because the adult video industry chose VHS instead of the technically superior Sony system. Pornographic computer games have also existed almost since the start of the industry - some of the earliest were Mystique's Atari 2600 video games, including Custer's Revenge, Beat 'Em And Eat 'Em and Gigolo. The Japanese company Hacker International, which also published games under the name Super PIG, produced several pornographic titles for the Nintendo Famicom. Three of these, renamed to Bubble Bath Babes, Hot Slots and Peek-A-Boo Poker, were distributed in the USA by Panesian. However, such games were for a while no longer produced very often for current consoles, largely due to the increased costs and potential legal problems associated with developing a game without the approval of the console manufacturer. With the release of BMX XXX, pornographic video games have again begun to be produced. Leisure Suit Larry and Playboy: The Mansion titles for game consoles feature pornography. However, pornographic games are now released mostly for personal computers, with Japanese pornographic games of various genres being the largest category. Erotic film producers are expected to play a major role in deciding the next DVD standard. Large outfits tend to support the high-capacity Blu-ray Disc, while small outfits generally favor the less-expensive HD-DVD.

It has long been theorized that there may be a link between pornography, particularly violent pornography, and an increase in sex crime. This theory has relatively little empirical support and indeed Japan, which is noted for violent pornography, has the lowest reported sex crime rate in the industrialized world. This has led some researchers to speculate that an opposite relationship may in fact exist: that wide availability of pornography may reduce crimes by giving potential offenders a socially accepted way of regulating their own sexuality. Conversely, some argue that reported sex crime rates are low in Japan because the culture is such that victims of sex crime are less likely to report it.

Pornographic work contains a number of conventions. Although pornography targeted at heterosexual males often includes interaction between females, interaction between males is taboo. In hardcore materials, a male generally ejaculates outside his partner's body, in full view. Penises are almost always shown fully erect. The choice of position is naturally geared to giving the viewer the fullest view of the woman, making the reverse cowgirl position, and the man holding the woman in a dog-and-lamp-post position among the most popular. Fellatio scenes usually involve the woman looking into the camera or at the man, for similar reasons. Especially in American or Japanese porn, women tend to be unrealistically vocal and loud during hardcore scenes. In the cheaper magazines the copy accompanying the text is often derogatory to the female subjects.

The legal status of pornography varies widely. Most countries allow at least some form of pornography and softcore pornography is usually tame enough to be sold in general stores and to be shown on TV. Hardcore pornography, on the other hand, is usually regulated. Child pornography is illegal almost everywhere and most countries have restrictions on pornography involving violence or animals. Some people, including pornography producer Larry Flynt and the famous writer Salman Rushdie, have argued that pornography is vital to freedom and that a free and civilized society should be judged by its willingness to accept pornography. Most countries attempt to restrict minors' access to hardcore materials, so that it is only available in adult bookstores, via mail-order, in some countries over special satellite TV channels, and sometimes in gas stations. There may be an age limit for entrance, or the materials are displayed partly covered. More generally, disseminating pornography to a minor is often illegal. Many of these efforts have been rendered moot by the wide availability of Internet pornography. There are recurring urban legends of snuff movies, in which murders are filmed for pornographic purposes. Extensive work by law enforcement officials to ascertain the truth of these rumors have been unable to find any such works. The potential ability to create realistic images using computer graphics or digital manipulation led to some debates on its legality. For instance, the Supreme Court of the United States struck down the Child Pornography Prevention Act of 1996 that prohibited, among other things, simulated child pornography. The court ruled that it violated the First Amendment to ban material depicting fictional illegal conduct when no such conduct had been involved in production. However, in the UK, the Criminal Justice and Public Order Act 1994 reached entirely the opposite conclusion, that if an image creates a convincing enough impression that it sexually depicts a child, it becomes an indecent pseudo-photograph of a child and is equally prosecutable under the law as an actual photograph. The Internet has also caused problems with the enforcement of age limits regarding performers. In most countries, women and men under the age of 18 are not allowed to appear in porn films, but in several European countries the age limit is 16. This material often ends up on the Internet and viewed by people in countries where this constitutes child pornography, creating challenges for lawmakers wishing to restrict access to such material.