President Obama has declared that the greatest terrorist threat which America faces is attacks by lone wolf terrorists. This volume expands the lone wolf rubric to include autonomous cells: small groups of terrorists who cooperate, but operate independently. The challenge presented by lone wolves and autonomous cells, unlike the threat emanating from established terrorist groups like Al Qaeda, has proven intractable because of the difficulty of gathering intelligence on these actors or effectively countering their actions. Lone wolves operate under the radar, staging deadly attacks such as that at the Boston Marathon, and the 2011 attacks in Norway. This volume includes Theory and Policy Studies, individual case studies and the technological impacts of chemical, biological and nuclear weapons as well as the impact of social media in the process of recruitment and radicalization.This book was originally published as a special issue of Terrorism & Political Violence.