Greater theoretical consensus and cohesion could offer critical insights for the broader community of international relations scholars into the role that gender plays in spawning and sustaining processes of violence. This review essay examines the role of gender in generating and perpetuating violence and aggression, both in theory and practice. I make four central claims. First, in many studies involving the role of sex and gender in violence, specific causal models tend to remain underspecified. Second, a divergence in fundamental assumptions regarding the ontological basis of sex differences implicitly permeates and shatters this literature. Third, arguments that men and women are more or less likely to fight appear too simplistic; rather, it is worth considering that men and women may possess different motivations for fighting, and fight under different circumstances and for different reasons. Finally, systematic differences in the variant psychologies of men and women regarding the relative merit of offense and defense exert predictable consequences for public opinion surrounding the conduct of war in particular.