The sex industry (also called the sex trade) consists of businesses which either directly or indirectly provide sex-related products and services or adult entertainment. The industry includes activities involving direct provision of sex-related services, such as prostitution, and sex-related pastimes, such as pornography, sex-oriented men's magazines, sex movies, sex toys and fetish and BDSM paraphernalia. Sex channels for television and pre-paid sex movies for on demand, are part of the sex industry, as are adult movie theaters, sex shops, and strip clubs.
Prostitution is a main component of the sex industry, and may take place in a brothel, at a facility provided by the prostitute, at a client's hotel room, in a parked car, or on the street. Often this is arranged through a pimp or an escort agency. Prostitution involves a prostitute or sex worker providing direct sexual services to a client. In some cases the prostitute is at liberty to determine whether she or he will engage in a particular type of sexual activity, but forced prostitution and sexual slavery does exist in some places around the world.
The legality of prostitution and associated activities (soliciting, brothels, procuring) varies by jurisdiction. And yet even where it is illegal there is usually a thriving underground business because of high demand and the booming revenue that can be made by pimps, brothel owners, escort agencies, and traffickers. 
The premises where people come to engage in sexual activity with a prostitute is a brothel,  though for legal or cultural reasons such premises may describe themselves as massage parlors, bars, strip clubs or by some other description. Sex work in a brothel is considered safer than street prostitution.
Prostitution and the operation of brothels is legal in some countries, but illegal in others. Even in countries where prostitution and brothels are legal, brothels may be subject to many and varied restrictions. Forced prostitution is usually illegal as is prostitution by or with minors, though the age may vary. Some countries prohibit particular sex acts. In some countries, brothels are subject to strict planning restrictions and in some cases are confined to designated red-light districts. Some countries prohibit or regulate how brothels advertise their services, or they may prohibit the sale or consumption of alcohol on the premises. In some countries where operating a brothel is legal, some brothel operators may chose to operate illegally.
Some men and women may travel away from their home to engage with local prostitutes, in a practice called sex tourism, though the destination pattern tends to differ between them. Male sex tourism can create or augment demand for sex services in the host countries, while female sex tourism tends not to use existing sex facilities. Like tourism in general, sex tourism can make a significant contribution to local economies, especially in popular urban centers. Sex tourism may arise as a result of stringent anti-prostitution laws in a tourist's home country, but can create social problems in the host country.
Businesses that offer prostitution services tend to cluster around military bases. The British naval port of Portsmouth had a flourishing local sex industry in the 19th century, and until the early 1990s there were large red light districts near American military bases in the Philippines. The Monto red-light district of Dublin, one of the largest in Europe, gained most of its custom from the British soldiers stationed in the city; indeed it collapsed after Irish independence was achieved and the soldiers left. The notorious Patpong entertainment district in Bangkok, and the city of Pattaya, Thailand, started as R&R locations for US troops serving in the Vietnam War in the early 1970s. Sex industries are also small but growing in several college towns.
The sex industry employs hundreds of people each day. These range from the sex worker, also called adult service provider (ASP) or adult sex provider, who provides sexual services, to a multitude of support personnel. Sex workers can be prostitutes, call girls, pornographic film actors, pornographic models, sex show performers, erotic dancers, striptease dancers, bikini baristas, telephone sex operators, cybersex operators, or amateur porn stars for online sex sessions and videos.
In addition, like any other industry, there are people who work in or service the sex industry as managers, film crews, photographers, website developers and webmasters, sales personnel, book and magazine writers and editors, etc. Some create business models, negotiate trade, make press releases, draw up contracts with other owners, buy and sell content, offer technical support, run servers, billing services, or payroll, organise trade shows and various events, do marketing and sales forecasts, provide human resources, or provide tax services and legal support.
Usually, those in management or staff do not have direct dealings with sex workers, instead hiring photographers who have direct contact with the sex workers. Pornography is professionally marketed and sold to adult webmasters for distribution on the Internet.
Pornography is the explicit portrayal of explicit sexual subject matter for the purposes of sexual arousal and erotic satisfaction. A pornographic model poses for pornographic photographs. A pornographic film actor or porn star performs in pornographic films. In cases where limited dramatic skills are involved, a performer in pornographic films may be called a pornographic model. Porn can be provided to the consumer in a variety of media, ranging from books, magazines, postcards, photos, sculpture, drawing, painting, animation, sound recording, film, video, or video game. However, when sexual acts are performed for a live audience, by definition it is not pornography, as the term applies to the depiction of the act, rather than the act itself. Thus, portrayals such as sex shows and striptease are not classified as pornography.
The first home- PCs capable of network communication prompted the arrival of online services for adults in the late 1980s and early 1990s. The wide-open early days of the World Wide Web quickly snowballed into the dot-com boom, in-part fueled by an incredible global increase in the demand for and consumption of pornography and erotica. Around 2009, the U.S. porn industry's revenue of $10–15 billion a year was more than the combined revenue of professional sports and live music combined and roughly on par or above Hollywood's box office revenue. 
Use of children
While the legality of adult sexual entertainment varies by country, the use of children in the sex industry is illegal nearly everywhere in the world.
Commercial sexual exploitation of children (CSEC) is the "sexual abuse by the adult and remuneration in cash or kind to the child or a third person or persons. The child is treated as a sexual object and as a commercial object".
CSEC includes the prostitution of children, child pornography, child sex tourism and other forms of transactional sex where a child engages in sexual activities to have key needs fulfilled, such as food, shelter or access to education. It includes forms of transactional sex where the sexual abuse of children is not stopped or reported by household members, due to benefits derived by the household from the perpetrator. CSEC is prevalent in Asia (Thailand, Cambodia, India) and parts of Latin America. Thailand, Cambodia, India, Brazil and Mexico have been identified as leading hotspots of commercial sexual exploitation of children. 
Adult entertainment is entertainment intended to be viewed by adults only, and distinguished from family entertainment. The style of adult entertainment may be ribaldry or bawdry. Any entertainment that normally includes sexual content qualifies as adult entertainment, including sex channels for television and pre-paid sex movies for "on demand", as well as adult movie theaters, sex shops, and strip clubs. It also includes sex-oriented men's magazines, sex movies, sex toys and fetish and BDSM paraphernalia.
The sex industry is very controversial, and many people, organizations and governments have strong moral objections to it, and, as a result, pornography, prostitution, striptease and other similar occupations are illegal in many countries.
The term anti-pornography movement is used to describe those who argue that pornography has a variety of harmful effects on society, such as encouragement of human trafficking, desensitization, pedophilia, dehumanization, exploitation, sexual dysfunction, and inability to maintain healthy sexual relationships.
Dolf Zillmann asserts that extensive viewing of pornographic material produces many sociological effects which he characterizes as unfavorable, including a decreased respect for long-term, monogamous relationships, and an attenuated desire for procreation.  He claims that pornography can "potentially undermine the traditional values that favor marriage, family, and children" and that it depicts sexuality in a way which is not connected to "emotional attachment, of kindness, of caring, and especially not of continuance of the relationship, as such continuance would translate into responsibilities"
Additionally, some researchers claim that pornography causes unequivocal harm to society by increasing rates of sexual assault,   a line of research which has been critiqued in "The effects of Pornography: An International Perspective" on external validity grounds,  while others claim there is a correlation between pornography and a decrease of sex crimes.   
Some feminists object to the sex industry, which they argue is exploitative to the women who work in it. They say it contributes to the male-centered objectification of women, increases sexual violence against women, and undermines gender equality. They argue that prostitution is a form of male domination and violence against women, and that in most cases it is not a conscious and calculated choice. They say that most women who become prostitutes do so because they were forced or coerced into it by a pimp or other human trafficker, or by circumstances such as extreme poverty, lack of opportunity, drug addiction, homelessness, and childhood sexual abuse. Based on these arguments, Sweden, Norway and Iceland have criminalized the buying of sexual services, while decriminalizing the selling of sexual services. (In other words, clients and pimps can be prosecuted for moneyed sexual transactions, but not prostitutes). These laws have greatly reduced illegal prostitution and human trafficking in these countries. 
Some feminists, such as Gail Dines, are opposed to pornography, arguing that it is an industry which exploits women and which is complicit in violence against women, both in its production (where they charge that abuse and exploitation of women performing in pornography is rampant) and in its consumption (where they charge that pornography eroticizes the domination, humiliation, and coercion of women, and reinforces sexual and cultural attitudes that are complicit in rape and sexual harassment). They charge that pornography contributes to the male-centered objectification of women and thus to sexism. However, other feminists are opposed to censorship, and have argued against the introduction of anti-porn legislation in the United States - among them Betty Friedan, Kate Millett, Karen DeCrow, Wendy Kaminer and Jamaica Kincaid. 
The sex industry often raises criticism because it is sometimes connected to criminal activities such as human trafficking, illegal immigration, drug abuse, and exploitation of children (child pornography, child prostitution). The sex industry also raises concerns about the spread of STDs.