+ What is Salafist jihadism?

	The March 11, 2004 attacks on a series of Madrid commuter trains killed 191 people.

Salafist jihadism is the name European scholars and counterterrorism officials have given to the prevailing ideology that inspires Al Qaeda and other Islamic radicals in Europe and elsewhere.

Salafists, also known as Salafis, are Islamic fundamentalists who believe that Islam should be restored to its most pure origins as written in the Quran. The majority of Salafists are not violent. As Prince Turki, the Saudi Arabian ambassador to the U.K., explained to FRONTLINE, "I am a Salafi and proud to be Salafi, and would consider most good Muslims who follow the teachings of the four principle imams of Sunni Islam are Salafis as well."

However, when Salafists meet and mingle with violent jihadists -- whose goal is to reestablish an Islamic state stretching from Morocco to the Philippines -- the ideologies fuse into a combustible mix.

Read more on the origins of Salafist jihadism and the emergence of its most dangerous incarnation.

+ Has Al Qaeda publicly threatened Europe?

Yes, multiple times. In April 2004, Osama bin Laden released a tape offering a truce to European countries who withdrew their troops from Muslim countries within three months. The offer was quickly rejected by governments throughout Europe.

In May 2003, Ayman al-Zawhiri, bin Laden's second-in-command, released an audiotape in which he said, "O Muslims, take matters firmly against the embassies of America, England, Australia, and Norway and their interests, companies, and employees. Burn the ground under their feet, as they should not enjoy your protection, safety, or security. Expel those criminals out of your countries."

In September 2004, Zawahiri released another tape threatening countries who had contributed troops to the war in Iraq. ''We shouldn't wait for the American, English, French, Jewish, Hungarian, Polish and South Korean forces to invade Egypt, the Arabian Peninsula, Yemen and Algeria and then start the resistance after the occupier had already invaded us,'' he said. ''We should start now."

+ Where do Europe's Islamic militants come from?

There is no one answer. Some arrive in Europe already radicalized from countries such as Egypt. Recent media reports have indicated that Iraqis and others tied to the insurgency against U.S.-led forces in Iraq have been active in Europe.

Others originated as peaceful immigrants among the millions who have emigrated from North Africa and elsewhere since the 1950s. Many of the radicals are second- and third-generation Europeans. There are also a few cases in which Muslim converts of European descent have turned to militancy.

+ Why are European Muslims becoming radicalized?

Only a small percentage of Muslims -- who represent the continent's largest and fastest growing religion -- resort to violent radicalism. For those that do, usually their feelings of cultural alienation and discrimination have left them vulnerable to extremist ideologies.

Some say initiatives like France's headscarf ban in public schools and the deportation of radical imams from a number of European countries serve to inflame the tensions and further alienate the Muslim community. Anthropology professor Paul Silverstein of Reed College has studied Algerian immigrants to France and says these state efforts are bound to fail, as they are "largely perceived by many French Muslims, if not Muslims worldwide, as attacks on Islam."

Europe's physical location -- within driving distance to various hot spots including Iraq, Afghanistan, Bosnia, and Chechnya -- leaves it vulnerable to jihadis returning from these conflicts that cannot or choose not to return to their countries.

Read more about the culture clash between Muslims and European secularism.

+ Why should Americans be concerned about terrorism in Europe?

Islamic militants use Europe as a logistical base and a source of recruits and money. After Sept. 11, investigators traced hijacker Mohamed Atta and other suspected Al Qaeda members behind the attacks to a cell Hamburg, Germany. A plan to bomb the Los Angeles International Airport at the turn of the millennium originated in Europe, and Richard Reid, who tried to blow up a Paris-to-Miami flight with explosives hidden in his shoe, is a British citizen. More recently, counterterrorism operations have uncovered a network that funneled recruits from Europe to fight against U.S.-led forces in Iraq.

The creation of the borderless European Union has also had consequences for counterterrorism efforts both within the E.U. and for the U.S. A terrorist with the proper papers can easily slip in and out of European countries. Under the Visa Waiver Program, which allows citizens and permanent residents of most European countries to travel to the U.S. virtually unrestricted, terrorists can more easily cross U.S. borders. Both Richard Reid and Zacarias Moussaoui, a French citizen indicted as a co-conspirator for 9/11, traveled to the U.S. under the Visa Waiver Program.

Is the Visa Waiver Program a security threat? Read more on the pros and cons.

+ How effective have European counterterrorism efforts been at stopping attacks?

It's difficult to gauge success by the numbers. Law-enforcement agencies throughout Europe have arrested hundreds of suspected terrorists since Sept. 11, but arrests don't always correspond to specific thwarted attacks. The secretive nature of counterterrorism also obscures what threats have been averted.

Over the years, some thwarted attacks have become public, including a plan to crash a hijacked airplane into the Eiffel Tower in 1994; threats against U.S. embassies in Paris and Rome; and a scheme to drive a truck bomb into Spain's National Court in 2004.

Overall success can be measured by the absence of attacks. Except for the Madrid train bombings of March 2004, Europe has been fairly free of tragedy on a large scale.

Read a chronology of some of the attacks that have been thwarted.

+ How does Europe fight terrorism?

Each country has its own police, intelligence, and court system, so there is no one answer. However, since 2001, the European Union has tried to make it harder for terrorists to take advantage of lax laws in one country or another. Countries across Europe are unifying their laws against terrorist financing, association with named terrorist groups, and immigration violations. Many countries also have preventive detention laws, and some have laws under which they can hold people for merely associating with a named terrorist group, regardless of whether they have taken part in criminal activities.

The European Union has a new counterterrorism leader, Gies de Vries, whose post is similar to the U.S. director of homeland security, but he has no power over police forces, regulations, or funding.

+ How do European counterterrorism strategies differ from those of the U.S.?

Since 9/11, European countries have largely pursued criminal prosecutions against suspected terrorists. The U.S. has pursued a "war on terror" with a policy of detaining suspected terrorists as enemy combatants without access to courts or lawyers. This distinction has made it difficult for some European countries to prosecute accused terrorists in their own countries because of a lack of access to witnesses held as enemy combatants in the U.S.

The United States has sometimes had to change aggressive counterterrorism efforts in response to European concerns. For example, it had to change its approach to screening overseas air travelers in order to protect passenger privacy.

Read more on the tensions in the trans-Atlantic relationship that have developed out of the difference in counterterrorism strategies.

+ Are some European countries faring better than others in integrating their Muslim communities?

Florida State University Professor Alec Hargreaves, author of numerous books on the North African immigrant community in France and currently a visiting professor of immigration and integration at the Sorbonne in Paris, gives high marks to the U.K. "British policy has generally been more accommodating than that of France or Germany," he says. "Given the large geographical distances separating the U.K. from Pakistan and Bangladesh (the two main Muslim states among the countries supplying Britain with migrant labor), it was unrealistic to think of those migrants as temporary residents. Instead, family settlement was more obviously the norm." Britain also led the way among Western European states in the 1960s and 1970s in developing anti-discrimination policies, which other European Union countries, such as France, are only just beginning to catch up with, he says.

+ Why do European Muslims seem to be becoming more radical than Muslims in the U.S.?

The answer is very simple, according to former CIA caseworker Marc Sageman. "The neglected part of this story since 9/11 is the almost heroic conduct of the American Muslim community," Sageman says. "Despite the fact that there was a lot of discrimination that happened to them after 9/11, they have never stopped being patriotic Americans. … It's why we haven't had anything here in the last three years -- and most of the threat came from the outside. They have been very cooperative with the FBI and law enforcement to try to root out this virulent distortion of Islam which is propagated by Salafi terrorists."

Read an interview with Marc Sageman in which he explains Al Qaeda's evolution and the new face of the global jihad.

+ How extensive is the use of the Internet by Al Qaeda and other jihadist terrorist groups?

According to statements made in the press by Gabriel Weimann, a senior fellow at the U.S. Institute of Peace and a professor at Haifa University, there are more than 4,000 terrorist Web sites. That's up from 12 known Web sites when he started keeping track in 1997. He says that all major terrorist groups now have a Web presence.

Read more on how terrorists are using the Internet.

+ What laws regulate terrorism financing in Europe?

After 9/11, the European Union updated its laws so that E.U. member states are required to share information on suspected financial backers of terrorism and to coordinate their law enforcement efforts with banks and other financial institutions. Additional E.U. measures require greater regulation and transparency of charities and non-profit organizations and closer monitoring of individuals carrying cash across E.U. borders.

Further, all E.U. countries must adopt by July 2005 the recommendations for preventing terrorism financing made by the Financial Action Task Force (FATF), an international organization. FATF measures call for countries to pass laws that criminalize terrorist financers and organizations, mandate the reporting of financial transactions linked to terrorism, and require better customer identification with international and domestic wire transfers.

Also, under the 1999 United Nations International Convention for the Suppression of the Financing of Terrorism, U.N. member states are required to prevent the financing of terrorists through charities and other organizations, to hold terrorist financiers legally liable, and to cooperate in the identification and seizure of terrorist funds.

Read more about the challenges facing U.S. and European officials as they try to crack down on terrorist financing.