Pornography has changed unrecognizably from its so-called golden age—the period, in the sixties and seventies, when adult movies had theatrical releases and seemed in step with the wider moment of sexual liberation, and before V.H.S. drove down production quality, in the eighties. Today’s films are often short and nearly always hard-core; that is, they show penetrative sex. Among the most popular search terms in 2015 were “anal,” “amateur,” “teen,” and—one that would surely have made Freud smile—“mom and son.” Viewing figures are on a scale that golden-age moguls never dreamed of: in 2014, Pornhub alone had seventy-eight billion page views, and XVideos is the fifty-sixth most popular Web site in the world. Some porn sites get more traffic than news sites like CNN, and less only than platforms such as Google, Facebook, Amazon, and PayPal. The twenty-first-century porn kings aren’t flamboyant magazine owners like Larry Flynt, whose taboo-breaking Hustler first published labial “pink shots,” in the mid-seventies, but faceless tech executives. The majority of the world’s tube sites are effectively a monopoly—owned by a company called MindGeek, whose bandwidth use exceeds that of Amazon or Facebook. Its C.E.O. until recently was a German named Fabian Thylmann, who earned a reported annual income of a hundred million dollars; he sold the company while being investigated for tax evasion.

The millions of people using these sites probably don’t care much about who produces their content. But those who work in porn in the United States tend to draw a firm line between the “amateur” porn that now proliferates online and the legal adult-film industry that took shape after the California Supreme Court ruled, in California v. Freeman (1989), that filmed sex did not count as prostitution. Since then, the industry has been based in Los Angeles County’s San Fernando Valley, where its professional norms and regulations have mimicked its more respectable Hollywood neighbors. In “The Pornography Industry: What Everyone Needs to Know” (Oxford), Shira Tarrant explains how that industry works in the new age of Internet porn, and sets out to provide neutral, “even-handed” information about its production and consumption.

It’s not an easy task. Since the “porn wars” of the seventies and eighties, when feminists campaigned against the expanding pornography industry (and other feminists sided with Hustler to defend it), talking about pornography in terms of mere facts has seemed impossible. The atmosphere of controversy makes it hard to avoid moral positions. Even to suspend judgment may be to take sides.

In 1995, the porn actress Jenna Jameson signed her first contract with a new porn studio called Wicked Pictures. She was twenty, ambitious, and already making a name for herself. In her memoir, “How to Make Love Like a Porn Star” (2004), she recalled meeting the studio’s founder in a rickety corrugated-steel office in an industrial park. “The most important thing to me right now is to become the biggest star the industry has ever seen,” she told him. “So you can either sign me or I can go to another company and take them to the top. It’s up to you. I’m going to be a star with or without you.”

Jameson and Wicked found each other at the right time. There had, of course, been stars before her. Linda Lovelace’s performance in “Deep Throat,” in 1972, made porn mainstream; later, her denunciation of the movie, which she characterized as filmed rape, made the idea of the porn star as victim mainstream, too. In the mid-eighties, the revelation that Traci Lords had been underage in her most famous films led to the prosecution of producers, agents, and distributors under child-pornography statutes, and new legislation resulted in stricter age-verification requirements for porn actors. But by the time Jameson arrived on the scene the industry had become an efficient star-making machine. It had distributors and advertisers, production teams and industry magazines, shoots requiring permits, agents who sold the talent and trade associations who represented them. Jameson quickly achieved her ambition, becoming the industry’s biggest star and most reliable brand. By 2005, her company, ClubJenna, had an annual revenue of thirty million dollars.

Things are different now. Much online porn is amateur and unregulated. It’s hard to tell how much, because there’s little data, and even larger studios now ape the amateur aesthetic, but applications for porn-shoot permits in Los Angeles County reportedly fell by ninety-five per cent between 2012 and 2015. Now most films have low production values, and they are often unscripted. Sometimes you can hear the director’s voice; apparently, many viewers can make do without the old fictional tropes of doctors and nurses, schoolgirls, and so on—the porn industry itself having become the locus of fantasy. Where performers like Jameson had multi-film contracts with studios like Wicked or Vivid Entertainment, such deals are now rare, and most performers are independent contractors who get paid per sex act.

Tarrant’s book sheds useful light on the bargain-basement world of contemporary porn. In 2012, one agent claimed that the actresses he represented received eight hundred dollars for lesbian scenes, a thousand for ones with a man, twelve hundred or more for anal sex, and four thousand for double penetration, but there’s reason to think that these figures are inflated. Stoya, a well-known performer who has written about her life in the industry, has cited a rate of just twelve to fourteen hundred dollars for double penetration. Wages have declined across the board. Tarrant estimates that a female performer filming three anal scenes a month would make forty thousand dollars a year.

Riskier acts are incentivized. According to one analysis of an industry talent database, women entering the business now will do more, and more quickly, than they once did: in the nineteen-eighties, they would wait an average of two years before a first anal scene; now it’s six months. Jameson famously never did anal (though one of her most viewed Pornhub clips is “Jenna Jameson accidental anal,” which shows, in slow motion, that on the Internet there’s no such thing as never). From 2000 on, she had only one onscreen male partner—her husband. “I look at these new girls today and I think, What the hell are they doing?” she said in 2004. “These girls don’t know that you have to start slow, baby, and make them pay you more for each thing you do.”

Today, most porn actresses don’t stick around long enough to start slow. The average career is between four and six months. Performers work long hours with no benefits and they have to cover significant out-of-pocket costs. Tests for S.T.D.s can be as much as two hundred dollars a month. Add to this grooming, travel, and the usual freelancer expenses and it costs a lot to be legal in the porn industry.

In a context of declining wages and rising costs, attempts at regulation are unpopular. In 2012, Los Angeles County passed Measure B, a law mandating condom use in porn shoots there. Advocacy organizations for performers have resisted the measure, saying that it ignores the preferences of their workforce and would compel performers to use not only condoms but also safety goggles and dental dams. More important, perhaps, it also ignores consumer preferences: in an age when few pay for porn, producers don’t want to alienate those who do. The regulated industry has developed other ways to avoid condoms—preëxposure treatments, production moratoriums when infections are detected, and, in some gay studios, a working assumption that performers are H.I.V. positive. Other producers, rather than comply, have left California for Nevada or Florida. The industry may have created the norms that dominate online porn, but it’s being squeezed into irrelevance, and preferences have taken on a life of their own.

So it is that, even as the Internet has made pornography ubiquitous, the industry itself, at least as Tarrant describes it, is in severe decline. Like the music business—where albums have been disaggregated into individual tracks sampled on YouTube or bought on iTunes—porn today is a plethora of thumbnail clips from which users pick and choose. And, just as many musicians treat recording as a loss leader in a career built on live performance and merchandising, many porn performers supplement their earnings with various forms of offscreen sex work.

Whether you see porn as just another sector disrupted by the Internet or as a still powerful engine of profit-driven exploitation depends on a thornier set of debates that shape how pornography is understood. To talk about porn purely in terms of costs and incentives is not, as Tarrant suggests, neutral. Even to stress the work involved is a political move.

When America’s pornographic secrets have been publicly aired, they have usually taken the form of First Amendment issues. In 1988, the Supreme Court overturned a ruling against Hustler that had awarded damages to the evangelical pastor Jerry Falwell, the founder of the conservative organization the Moral Majority. (The magazine had published a satirical ad in which Falwell described his “first time” with his mother.) Flynt became an unlikely liberal hero, cementing a coalition between free-speech defenders and pornographers. After California v. Freeman, the Adult Film and Video Association of America renamed itself the Free Speech Legal Defense Fund, and, later, the Free Speech Coalition.

But, in the famous phrase of the legal scholar and anti-pornography campaigner Catherine MacKinnon, pornography is not “only words.” The feminist campaigns of the seventies against rape and violence against women condemned pornography not on the ground of obscenity but on the ground of harm. It wasn’t a private matter but a political expression of male power. As MacKinnon wrote, with the anti-pornography feminist Andrea Dworkin, pornography was “the graphic sexually explicit subordination of women.” Dworkin described it as a form of sexual slavery.

“Lovelace was her slave name,” the protest banners of anti-pornography feminists read, after Lovelace published her memoir, “Ordeal,” in 1980. Pornography, they said, sexualized subordination, dehumanized women, and tricked them into objectifying themselves to please men. Not only did it depict and provoke violence but it was, in itself, a violent act, committed not just against the women involved in its making but against all women. In the early eighties, MacKinnon and Dworkin fought for ordinances to enable suits for sex discrimination by anyone who could prove harm through pornography. In an alliance with conservative Christian groups, they got one passed in Indianapolis, though it was soon struck down.

The anti-pornography arguments often described women as victims, without agency, but “pro-sex” feminists argued that women should be able to use, and make, porn. So long as it was consensual, it might also be empowering. Some saw porn as part of an emancipatory project to reclaim female pleasure and to assert a sexuality that had been denied them. Lesbian, gay, and queer defenders saw porn as an opportunity to challenge sexual norms and taboos. For them, the definition of porn as female subordination by men mirrored conservative puritanism. It ignored the medium’s radical potential—how consensual B.D.S.M. could subvert power structures, or how erotic displays of imperfect or disgusting bodies could be a Rabelaisian weapon in a war against élite prudery.

Other defenders of porn conceded that it was exploitative and infused with fantasies of domination, often involving classist and racist tropes. But they objected to using the law to police sexuality and also worried about the implications of anti-pornography arguments. When feminists said that excessive porn use made men unable to tell the difference between violent sex on the screen and intimate sex in real life, which men did they mean? Not so much their husbands or their friends but other men—men somewhere else, men less in control of their (supposedly innate) violent tendencies, poorer men. Such assumptions rested on the very same prejudices that porn made use of, and erred in supposing that viewers couldn’t distinguish fantasy from reality. Besides, pornography had to be read as part of a culture that was already full of objectification. Perhaps it was as much a symptom of violence as its cause.

Thirty years later, porn is more pervasive than ever, but it’s also more diffuse—and so are the debates. There are new organizations like Stop Porn Culture, led by the feminist Gail Dines, which campaign for porn’s abolition, and against the industry’s hypersexualization of women and the “pornification” of culture. Old coalitions have reappeared, deploying new rhetoric: in April, Dines supported a Republican bill in Utah that declared pornography not a moral threat but a “public health hazard.” Critics worry as much about men’s health—porn addiction, erectile dysfunction—as they do about violence against women.

Pornography’s defenders still lean on ideas of sexual freedom and empowerment. “I am a pervert,” Sasha Grey—the only recent star to rise anywhere near Jameson’s heights—declared in a 2009 interview. “I want to tell young women that sex is O.K. It’s O.K. to be a slut. You don’t have to be ashamed.” In a “mission statement” she wrote when she entered the industry, at eighteen, Grey said that she was “determined and ready to be a commodity that fulfills everyone’s fantasies.” She was no Lovelace: “If I am working out any issues through porn, it’s anger at society for not being open about sex.”

Performers now often defend porn using the language not of freedom but of work, and begin with the idea that sex work is a form of work like many others. Sure, working in the sex industry is exploitative and precarious, but so is work in other industries. The porn workers who do their jobs well enough that you buy their performance are giving their consent, but they likely do so only as other precarious workers do: they need the money and have limited choices. To an older generation of feminists, this defense sounds hollow: it concedes that sex and intimacy can be bought and sold. For a younger generation, the idea that they can’t is a misunderstanding: sex has long been monetized, and today there’s nowhere that the market doesn’t go. To reflect this, many younger feminists want a sexual politics that restores a tradition of labor organizing predating the porn wars (when even Playboy bunnies had a union), and seek to protect performers from profit-seeking managers.

At the fringes of the industry, performers are trying to change it from the inside, in the name of fair pay, better conditions, and more enjoyable sex. The aim of companies like Pink and White Productions and TrenchcoatX is to challenge the tube sites’ monopoly and to overthrow the racist, sexist categories that silently shape preferences. Their hope is that making inclusive, diverse porn—in which the performers’ pleasure is authentic and the orgasms real—will change sex for the better. The defense of this artisanal approach to porn pulls in contradictory directions: it at once argues that porn is work and not pleasure, and also that the pleasure it captures is authentic. Tarrant, despite claiming neutrality, is subtly allied with this view, and compares campaigns for ethical porn to those for organic, fair-trade food. In reality, it’s a harder sell. Few people want ethics with their porn.

Describing porn production as work is an important strategy to protect workers’ rights. But it leaves open the question of pornography’s effects. Abolitionists say there is overwhelming proof that it provokes violence and is bad for our health. Pro-porn campaigners say there are no reliable data either way, as does Tarrant. They’re not wrong: each side commissions its own surveys, has its own journals, and cites selectively. There are studies for everything—to show that pornography consumption correlates with aggressive behavior, that performers are victims of sexual abuse, and that such findings are premised on ill-founded stereotypes and stigmas.

When it comes to sexual practices, too, statistics are open to interpretation. Anti-pornography campaigners frequently cite the widely reported increase in the practice of anal sex among heterosexuals as evidence of porn’s influence. (In a 2014 study of anal sex among young British heterosexuals, a majority of young men surveyed—described as “teen-age boys” by the anti-porn camp, and “emerging adults” by the pro—admitted “persuading” their female partners to try it, with reluctant or little consent.) The campaigners insist that teen-agers are reënacting humiliations they’ve learned online. But that assumption leaves out other explanations. The British study suggested that the rise of premarital sex has meant that “conquest” narratives, which once fetishized the taking of virginity, now require a new focus. Equally, it might indicate a severance between reproduction and sex, or a straight acceptance of gay sexuality.

Sometimes, though, porn’s defenders overcompensate. They are too ready to interpret the lack of unequivocal data about porn’s impact as unequivocal proof that there is no impact. In a field as hard to measure as sexual behavior, this seems unwise. Pornography may be more likely to turn us into solipsistic masturbators than violent rapists, but it’s hard to imagine that it has no effect at all. The pro-porn argument, which insists that pornography is changing but denies that it changes us, appears contradictory. It inverts the anti-porn mistake of seeing porn as the key engine of transformation, instead giving it no power whatsoever. But sex is always changing, and, though porn can’t explain it all, its role can’t be ruled out, either.

“Our flesh arrives to us out of history, like everything else does,” Angela Carter wrote. “We may believe we fuck stripped of social artifice; in bed, we even feel we touch the bedrock of human nature itself. But we are deceived.” Today, our flesh comes to us from the Internet, and not only what we consume but how we consume has changed since the porn wars. Porn is abundantly more, in every way: there are more people, more acts, more clips, more categories. It has permeated everyday life, to the point where we talk easily of food porn, disaster porn, war porn, real-estate porn—not because culture has been sexualized, or sex pornified, but because porn’s patterns of excess, fantasy, desire, and shame are so familiar.

Despite porn’s ubiquity, the Internet has also made it more private, and its effects less knowable. The consequences of seeing sex before having it are as unclear as those of Facebook’s colonization of our leisure time. Pornography isn’t hermetically sealed from the rest of culture, and today it sits on a continuum with other problems of technology that we don’t yet know how to address.

Pornography helped shape the Internet—for instance, with its need for high-bandwidth technology—and it reflects and magnifies its trends. The triumph of porn has come at a cost to the industry itself, which can no longer produce a Jenna Jameson. Despite MindGeek’s near-monopoly of the tube sites (which, like other Internet platforms, are underregulated), their content is increasingly crowd-sourced. Mass production in the San Fernando Valley has been replaced by an amateur landscape in which everyone is a potential producer, and in which our fantasies and worst aspirations—our greed, our desire to humiliate, to dominate—are fed back to us in larger quantities than ever before. Decentralization hasn’t led to diversification (except at the margins, where buying ethical porn is like buying vinyl). Most porn remains conservative, brutal, and anonymous. It’s rapid-fire, often monotonous, and even if, or because, it does the trick, much of it is pretty depressing. It’s hard to see how local protests, however admirable, can resist a business model that already profits from decentralized, unregulated, amateur production. Except for the few companies that have profited from distribution, it’s unclear who makes money from porn, and how that money connects either to the work of performers or to how they are treated. With the decline of the industry, pornography, like the Internet itself, seems ever harder to control. Some will find that cause for horror, others, for celebration. Every era gets the porn it deserves.

[Katrina Forrester teaches history at Queen Mary University of London.]