This article describes how Bruce Hoffman and Marc Sageman, two prominent scholars of terrorism, square off over whether Al Qaeda remains the primary global terrorist threat. The dispute began in the pages of "Foreign Affairs," where Hoffman, a professor in the security-studies program at Georgetown University, wrote a withering review of Sageman's recent book, "Leaderless Jihad: Terror Networks in the Twenty-First Century" (University of Pennsylvania Press). Hoffman's main knock on Sageman, a sociologist and former CIA case officer who is now the first scholar in residence with the New York Police Department, is that his book understates the threat still posed by Al Qaeda and its leader, Osama bin Laden. Sageman argues that while Al Qaeda remains a menace that must be confronted, the real threat to the West is now much more diffuse, homegrown, and self-organizing than it was in 2001. Islamic terrorism has evolved over the past few years into a new wave of largely autonomous Al Qaeda sympathizers--"bunches of guys," Sageman calls them--who hatch their plots over the Internet and from within Western countries. Hoffman counters that because Al Qaeda's leadership has reconstituted itself in Pakistan's tribal frontier region, bin Laden and his top deputies should remain the primary focus of American military and intelligence efforts.