Does the security of women influence the security and behavior of states? Existing evidence linking the situation of women to state-level variables such as economic prosperity and growth, health, and corruption is fairly conclusive. Questions remain, however, concerning the degree to which state security and state security-related behavior is linked to the security of women. The “women and peace” thesis draws upon evolutionary biology/psychology for ultimate causes of this linkage, and sociological theories of social diffusion and psychological theories of social learning for more proximate causal mechanisms. Together, a new data resource—the WomanStats Database—and conventional methodology find a robust, positive relationship between the physical security of women and three measures of state security and peacefulness. In addition, a comparison of this proposition to alternative explanations involving level of democracy, level of economic development, and civilizational identity shows that the physical security of women is a better predictor of state security and peacefulness. Although these results are preliminary, it is still possible to conclude that the security of women must not be overlooked in the study of state security, especially given that the research questions to be raised and the policy initiatives to be considered in the promotion of security will differ markedly if the security of women is seriously considered as a significant influence on state security.