We conducted a systematic review of the contemporary scientific literature to (a) identify consensus, where it exists, regarding factors associated with membership in terrorist organizations and/or perpetration of terrorist attacks; (b) drive future research directions; and (c) inform evidence-based counterterrorism strategies. Systematic searches of 6 databases identified 205 articles that met inclusion criteria. Of these, 50 articles reported on findings of empirical research, 24 reported inferential statistics, and 6 of these compared characteristics of known terrorists to nonterrorists. Across various aspects of terrorism and terrorists (e.g., type of terrorist, attack type), articles rarely specified their focus. When examined factors typically focused on characteristics of the individual. Review of the empirical findings suggest 9 variables with at least some support for their association with terrorism: age, socioeconomic status, prior arrest, education, employment, relationship status, having a grievance, geographic locale, and type of geographic area. However, given the limitations of the research, there is insufficient evidence to conclude that any of these variables are empirically supported risk factors. Findings identified additional characteristics of an individual (i.e., country of birth, Islamic faith, military experience, foreign travel history, family or friend in a terrorist or extremist organization) and their environment (i.e., income inequality, media and government influences) that merit further evaluation. Findings also emphasized the importance of a triggering event. Finally, findings indicate that some widely accepted “risk” factors have limited empirical support for their association with terrorism. A focus on these factors might contribute to discrimination and reduce the effectiveness of counterterrorism strategies.