Recent terrorist attacks highlight the threat of terrorist violence authored not by recognized terrorist groups, but by unaffiliated individuals. In a number of cases, these individuals appear to have been motivated by extremist literature and Internet posts. Attacks in the United States and abroad illustrate the potential for radicalized individuals, acting alone or in small groups, for authoring significant damage. For many, the radicalization process began or was enhanced by appeals for action engendered in calls for leaderless resistance or leaderless jihad. The leaderless resistance literature of the radical right and the leaderless jihad literature of Islamist terrorism are compared to identify common themes in problem recognition, level of involvement, and constraint recognition. While there are similarities, differences remain largely in how problems are presented, constraints on action are characterized, and conceptions of constituencies.