Pornography (often shortened to porn or porno) has been defined as sexual subject material "such as a picture, video, or text," that is considered sexually arousing. Indicated for the consumption by adults, pornography depictions have evolved from cave paintings, some forty millennia ago, to virtual reality presentations in modern-day. Pornography use is considered a widespread recreational activity among people in-line with other digitally mediated activities such as use of social media or video games. A distinction is often made regarding adult content as whether to classify it as pornography or erotica.

Depictions of a sexual nature have existed since the times of prehistory. The oldest artifacts that are considered pornographic were discovered in Germany in 2008 CE and are dated to be at least 35,000 years old. Throughout the history of erotic depictions, various groups within society have regarded them as noxious and made attempts to suppress them under obscenity laws, censor them, or make them illegal. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. The Indian Sanskrit text Kama Sutra, written in the 3rd century CE, contained prose, poetry, and illustrations regarding sexual behavior, and the book was celebrated; while the British English text Fanny Hill (1748) by John Cleland, considered to be "the first original English prose pornography," has been one of the most prosecuted and banned books in history. In the late 19th century, a film by Thomas Edison that depicted a kiss was denounced as obscene in the United States, whereas Eugène Pirou's 1896 film Bedtime for the Bride was received very favorably in France. Starting from the mid-twentieth century on, societal attitudes towards sexuality became more lenient in the Western world, and legal definitions of obscenity became more limited. In 1969, Blue Movie by Andy Warhol, became the first film to depict unsimulated sex that received a wide theatrical release in the United States. This was followed by the "Golden Age of Porn" (1969–1984), a time period when many high quality pornographic films played in theaters, and became part of popular culture. The introduction of home video and the World Wide Web in the late 20th century led to worldwide growth in the pornography business. Starting in the 21st century, greater access to the internet and affordable smartphones among people enabled pornography to become more culturally mainstream.

Pornography has been notable for providing a safe outlet to sexual desires that may not be satisfied within relationships and for being a facilitator of sexual release in people who cannot or do not want to have a partner. Pornography is often equated with Journalism as both offer a view into the unknown or the hidden aspects of a human society. Research has suggested four broad motivations for people to use pornography, namely: "using pornography for fantasy, habitual use, mood management, and as part of a relationship." People in general view pornography for various reasons; ranging from a need to enrich their sexual arousal, as an aid for masturbation, to facilitate orgasm, learn sexual techniques, reduce stress, alleviate boredom, enjoy themselves, see representation of people like themselves, explore their sexuality, know their sexual orientation, improve their romantic relationships, or simply because their partner wants them to. Pornography has been found to serve the purpose of an anti-depressant for the unhappy. Studies have found that sexual function defined as "a person's ability to respond sexually or to experience sexual pleasure," is better in women who consume pornography frequently than in women who do not. No such association has been found in men. As for pornography use to have any implication on public health, scholars have stated that pornography use does not meet the definition of a public health crisis. People who regard porn as sex education material were identified as being more likely to not use condoms in their own sex lives, a risky behaviour that is warned against considering the fact that performers working for pornographic studios undergo regular testing for sexually transmitted infections every two weeks, unlike much of the general public. Comparative studies have indicated that higher "pornography consumption" and "pornography tolerance" in people are associated with their greater support for gender equality; people who support regulated pornography are distinguished as being more egalitarian than those who support a ban on pornography. While some feminist groups sought to abolish pornography believing it to be harmful, other feminist groups have opposed censorship efforts insisting pornography is benign. A longitudinal study has ascertained that pornography use could not be a contributing factor in intimate partner violence.

Called an "erotic engine," pornography has been noted for its key role in the development of various communication and media processing technologies. By being an early adopter of innovations ahead of other industries and as a provider of financial capital, the pornography industry has been cited to be a contributing factor in the adoption and popularization of many technologies. The accurate economic size of the porn industry in the early twenty-first century is unknown. Kassia Wosick, a sociologist from New Mexico State University, estimated the worldwide market value of porn to be at US$97 billion in 2015, with the U.S. revenue estimated between $10 and $12 billion. IBISWorld, a leading industry market researcher, projected the total U.S. revenue to reach US$3.3 billion in the year 2020. In 2018, pornography in Japan was estimated to be worth over $20 billion. The U.S. pornography industry employs numerous performers along with production and support staff. It has its own industry-specific publications, XBIZ and AVN; a trade association, the Free Speech Coalition; and award shows, XBIZ Awards and AVN Awards. Apart from regular media coverage, the industry receives considerable attention from private organizations, government agencies, and political organizations. From the mid 2010's, unscrupulous pornography such as deepfake pornography and revenge porn have become issues of concern.