The French simply love it–pork sausages, pigs’ feet and ham. But when Mouhad Bourouis, 33, worked at a summer day camp for underprivileged children in the south of France a few years ago, charcuterie posed a problem. Out of 80 kids, 28 were Muslim and the halal restrictions on their diet, like kosher ones for Jewish children, meant they could eat no pork at all. “The first week I planned 28 meals with no pork, but it was just too expensive and too much of a hassle,” Bourouis recalls. “So the second week, I got all the parents together and told them I would plan meals that would be OK for all the kids. If they really wanted to eat sausage, they could wait to be back at the family dinner table.”

Bourouis, the son of Algerian immigrants and a prosperous attorney in Marseilles, tells the story to show how problems of integrating Muslims into French society can be overcome. But for many in France, and Europe, the tale also poses a deeper question–indeed, an existential one. How much will their societies be changed, willingly or not, by the need to accommodate their burgeoning Muslim populations? It’s not just a matter of bacon and sausage, of course, but of laws, lifestyles, mores, cultures.

The search for an answer, still far from conclusive, has emerged as the most passionately debated issue in European life. Not so long ago, Europe’s Muslims were left to wrestle with their own identity issues. Their job, as native Europeans saw it, was to assimilate–or not. That’s changed, utterly. Today the specter of terrorism, fairly or not, looms over the Continent’s Islamic communities; last week’s bombings in Turkey only intensified the fears and suspicions prevalent in many countries. That makes the question of how to integrate Europe’s Muslims both more critical–and far more difficult.

There are now more than 12 million people of Muslim origin in Western Europe, roughly half of them in France. Visiting the city of Marseilles, where nearly a third of the population is Arab, one sees the more familiar dimension of the phenomenon. The youths slouched against walls in the twisting, cobbled streets of the old port are three to five times less likely to have a job than their “French” counterparts. Whole neighborhoods could easily be in the Maghreb: many have little, if any, contact with the country beyond their walls. Among young men, particularly, Islam has turned from a faith into a rejection of the French system that many feel has failed them.

The real challenge, though, lies not with those who have checked out of the system, but those who want in, on their own terms. That’s the role of a new crop of twenty- and thirtysomethings–call them Generation M–who are Europeans in almost every sense of the word. Unlike their forebears, they are mostly born in Europe and claim it as their own society. They do well in school and the workplace and, often, have effectively “Christianized” their faith by making it a personal matter. “My religion is something private, something I don’t feel like sharing in public,” says Delilah Kerchouche, 30, a chic Parisian journalist whose immigrant parents raised her “as Algerian.” “But it’s definitely part of who I am.” Rather than struggling to “fit in,” these Gen Mers want Europe to make space for them, and as their numbers grow, Europe needs them to succeed.

In France, Kerchouche is a part of the “Beurgeoisie,” slang for bourgeois Beurs, or successful Maghrebi Arabs. In Britain, she would be a Yummie, or Young and Upwardly Mobile Muslim. They are confident, culturally ambidextrous, second- and third-generation Europeans, aware of their rights as European Union citizens. And critically, they are asserting the right to be both modern and Muslim, both European and Islamic. Swiss-born Tariq Ramadan, whose grandfather founded the revolutionary Muslim Brotherhood in Egypt, encourages these youths to seize their rights as citizens, and to forge alliances with other groups, including the anti-globalization movement. “Muslims in the West were waiting for answers from the so-called Islamic world,” says Ramadan. “That’s changed. Now girls in Spain and France are going to court to uphold their right to cover their heads in school, while the Arab European League in Belgium is demanding bilingual education for kids who speak Arabic at home.

Such efforts are forcing traditional Europeans to rethink their own ideas of cultural identity–and test the limits of their tolerance. France, for instance, fought a long battle to keep religion, in the form of Catholicism, out of its classrooms. Is it now to permit Muslim girls to wear headscarves? What will the famously laissez-faire Dutch do about ferociously intolerant Muslim preachers who say gays should be slaughtered like pigs? What will they do, a decade or two from now, when the majority of Dutch newborns will be Muslim?

France, with the largest Muslim population, is the great test case. Wave after wave of immigrants have been quietly integrated over the past 100 years by a system that was less melting pot than crucible. It refused to recognize any ethnic, racial or religious distinctions whatsoever among citizens whose right and duty was to share in France’s language, its republican values and its historical culture. Until recently the system worked, creating Frenchmen who were black and Frenchwomen who happened to be Jewish, but who didn’t threaten France’s civilization or identity. American-style multiculturalism, in this context, was considered a recipe for chaos.

That old system is collapsing under the weight of its own contradictions. In the last three months, nearly 100 cases arguing for a girl’s right to wear a headscarf to school have been brought before the French Ministry of Education. Earlier this month a multipartisan commission of M.P.s backed legislation banning all religious symbols from state-run institutions in France, and on Oct. 10 a court upheld the expulsion of Muslim sisters Lila and Alma Levy from a state school in Aubervilliers for wearing hijab. Human-rights campaigners, on the other hand, argue that banning the veil not only contravenes the new European human-rights charter but interferes with French constitutional guarantees of liberty. “They claim that nobody should force a woman to wear the hijab,” says Lila Levy, 18. “But how can they force us to remove it? If they really cared about our freedom, they should let us be free to decide whether we want to wear it or not.”

Similar battles are playing out elsewhere in Europe. Last February a 13-year-old Spanish immigrant, Fatima Eldrisi, won the right to go to public school in a hijab, after local education authorities agreed that her right to education was more important than what she wore. A parliamentary commission in the Netherlands gloomily observed that “integration with so-called allochtones [slang for Dutch Muslims] has failed.”

Critics in Britain, which prides itself on its freedom from a state-sponsored cultural identity, are quick to point out the downsides of a more laissez-faire approach–chief among them so-called Londonistan, the network of mosques and meeting halls notorious for harboring Islamic militants. There are many such places, among them a working-class neighborhood of the northern industrial city of Bradford, replete with halal butchers and tandoori restaurants. One 25-year-old man there, bearded with light green eyes, wishes to be identified only as Ahmed. He has a broad Yorkshire accent but says he’s an Afghan Pathan. “If you’re Muslim, you’re Muslim,” he says. “It doesn’t matter if you’re Afghan, British or European. There’s only one Islam.” Ahmed says he used to do drugs and hang out in clubs, before rediscovering his religion and getting a job in a factory building tanks and planes. This is his jihad, he says: “If you want to be a real man, and fight the real fight, you try to be a good Muslim when you’re in a place with naked women, with miniskirts, with casinos and guns. The real jihad is when you can control your tongue and your private parts.” In Britain, he notes, he’s free to do what he likes as a Muslim. His colleagues and friends are open-minded and tolerant, even reminding him when it’s time to pray.

That points toward part of the answer to Europe’s Islam question. The fact that most Muslims in Britain were automatically granted citizenship as Commonwealth members produced second and third generations certain of their right to participate in commercial, political and civil life. This is a far cry from some countries in Continental Europe, where state-sponsored secularism and unwillingness to recognize minorities, as in France, or narrow definitions of nationality, as in Germany, left Muslims for many years on the margins of society. To be sure, Britain is also plagued by discrimination. Two thirds of Muslim organizations reported unfair treatment in state schools and employment compared with other religious groups. Some 80 percent of Pakistani and Bangladeshi households have incomes at or below the national average, compared with 40 percent for other ethnic minorities. But at least British Muslims have schools, they’ve got civil liberties, they’ve got Muslims in the House of Lords. In Britain Gen M has undeniably entered the mainstream. Where their parents opened corner shops and halal butchers, they’ve moved into the civil service, doctors’ offices and even that bastion of British culture, the City. BBC Radio’s morning religious slot, “Thought for the Day,” features Muslim scholars as well as ministers. British schoolchildren now learn about Islam and Hinduism in religious-education classes. Prince Charles has toyed with changing his title from “Defender of the Faith” to “Defender of the Faiths.”

Thirty-year-old Sajid Hussain could be a poster boy for modern Muslim Britain. He’s Oxford educated, devout and as comfortable discussing big-bang theory as he is talking about medieval Muslim philosophy. Now he’s teaching science at a Bradford secondary school, as well as working to start a new Islamic girls’ school that will also welcome Jews and Christians–anyone who is not particularly comfortable with the sex education and liberal atmosphere in Britain’s secular schools. It is the ever-moving moral standard, he argues, on issues like dress, premarital sex and homosexuality that unnerves Muslims, just as it does religious Jews and Christians. “Secularism is not just a problem for Islam, but for all the big religions.”

As Muslims gain the political confidence to assert themselves, and the skills to forge alliances with other groups, their impact on European culture and society can only grow. Even the reluctant French government is realizing that life in a globalized world may mean that Muslims–and, indeed, religion itself–cannot be kept in purdah. Nor can the broad cultural identities associated with religion and ethnicity simply be denied. The devout and the doubting, the radical and the secular, all may think of themselves as “Muslim,” and more and more they will assume their rightful place in the arts and the media, in parliaments and on village councils, in board rooms and on military promotion lists.

Generation M is changing Islam from a foreign faith into a dynamic force for change that cannot be resisted any more than it can be predicted. Asma, a pretty green-eyed 16-year-old student at Averroes, France’s first Muslim school, in Lille, recalls having to remove her hijab when she went to her former high school. At Averroes, she can wear it–and no longer must hide herself behind the traditions of French secularism. It remains to be seen whether, when it comes time for her own daughter to decide to wear the hijab or not, that tradition may itself be gone. Along, perhaps, with charcuterie?