This study argues that the spread of violent extremism cannot be fully understood as an ideological or social phenomenon, but must be viewed as a process that integrates the two forces in a coevolutionary manner. The same forces that make an ideology appealing to some aggrieved group of people are not necessarily the same factors that promote its transfer through social networks of self-interested human beings.As a result, radicalization inexorably intertwines social and ideological forces in systemic fashion. The coevolutionary nature of the social and ideological spheres presents a unique challenge and is one of the reasons that rigorous efforts to identify a radical or terrorist profile have not yielded significant return. Efforts to develop an archetype often focuses on individual traits, but it may be that profiles based on social and ideological behavior need to be considered simultaneously in developing a theory that is actionable for counter-terrorism practitioners.Key insights from the theoretical and empirical discussions that follow provide new insights into the social patterns of violent extremists over time, which are important to understanding radicalization.The analysis of domestic terrorism data shows that, to date, there is little evidence of lone wolf jihadists. There are very few people who progress to violent action in isolation, and those that do so are often motivated by other forces such as mental health issues or other political grievances. Many radicals have a history of social contact or reaching out to develop relationships with like-minded individuals.Social relationships follow a nonlinear pattern. They are increasingly important in the early stages of radicalization and peak when people accept a violent doctrine. Developing new relationships becomes less important once individuals come to adopt radical beliefs. The empirical analysis suggests that the search for external validation of radical ideas is most important in the early stages of an individual's radicalization and declines in importance once the barriers to entry are overcome.There is also a nonlinear relationship observed in the data analyzed here between social ties and ideological affinity, whereby those primed for affinity through exposure to radical ideas in early schooling have as many close social ties as those with completely secular schooling. Individuals in between these two extremes averaged fewer close connections, which challenges conventional wisdom about ideological predisposition and social relationships.The importance of self-serving extremism has not been well recognized. Individualswho recruit others gain social status for their efforts, meaning that the spread ofextremism may be just as much a function of self-interest as ideological fervor. This hasimportant implications understanding and countering violent extremism.The growth of radical groups is a self-organizing process driven by aggregation ofindividual behavior, where the entry catalyst into an extremist cell most likely takes theform of someone who recruits one, two or three other participants. This self-organization produces cells that have many close-knit people, or can easily accessothers, meaning that such groups are well suited to facilitation and monitoring. Bycontrast, such cells are much less likely to have many gatekeepers or brokers whooperate between cliques.