Terrorists combining motivations and capabilities to conduct significant chemical, biological, radiological, or nuclear (CBRN) attacks are, logically and empirically, outliers. Certain characteristics of radical environmentalism heighten the risk of such outliers. The majority of even radical environmentalists embrace nonviolence. Those who turn violent mostly do so in limited ways due to a combination of motivations and capabilities. Fringe elements are motivated to commit large-scale—including CBRN—violence, but are mostly constrained by capability. Yet eco-radicalism also draws more capable adherents. If serious CBRN terrorism attacks occur—a risk about which analysts differ markedly—radical environmentalist fringe actors are plausible perpetrators.