A profile of the international terrorist network that the United States has singled out as the most serious threat to U.S. security.

President Obama vowed in January 2009 to close the prison camp at Guantanamo Bay. Two years later, the White House continues to face challenges to that promise, leaving critics to suggest the facilit…

An increase in terror incidents involving Islamic radicals who are U.S. citizens is vexing law enforcement officials and posing new questions about the roots of their radicalization.

Western Europe’s burgeoning Islamic population continues to spark concerns about Muslim assimilation and a cultural divide.

Pakistan’s intelligence agency, the ISI, faces persistent accusations of links to terrorism, despite repeated denials.