This chapter addresses three questions: How is the terrorism of today organized?  How does it differ from the terrorism of the past? What are the policy implications?  Contemporary terrorism is diverse as well as diffuse, involving different patterns of organization rather than a single model. It is also not entirely new, as the precedents of nineteenth century anarchists and twentieth century far right extremists demonstrate. The emerging organizational framework of jihadist terrorism evolved from the dissolution of Al Qaeda in the aftermath of the American government’s response to the 9/11 attacks.  The jihadist threat poses a serious yet poorly understood challenge for democratic governments. The loose and shifting structure of terrorism makes it extremely difficult to prevent attacks.