Behavior at the extremes is the proving ground for all theory. Applying Gender Theory to the violent crime of terrorism reshapes our thinking about this socially central phenomenon. As with crime generally, the violence and social significance of New Terrorism meant that initially, its “maleness” was taken for granted. Through a case study of 9/11, we demonstrate how “hegemonic masculinity,” rather than mere maleness, underscored both the attack and the responses to it. But the historic and increasing involvement of women in terrorism now challenges traditional assumptions about women’s apparently more “peaceable” nature. A case study of the abrupt inclusion of women into the front line of terrorism shows how persistent stereotypes in target societies are exploited by terrorist organizations to achieve their strategic objectives. And, as with all “unfemale” crime, gender stereotypes still dominate media portrayals of women terrorists as well as the social science quest to explain the motivation of terrorists. There is, though, no denying that unequal power relations mean that women fare worse than men as perpetrators, victims, and citizens. We conclude that Gender Theory not only recasts our understanding of terrorism, but also forces us to sharpen criminology’s theoretical toolkit.