Rapid developments in technology – ranging from gene editing to cognitive manipulation to computer-brain interfaces – are rendering virtually every aspect of human beings contingent and subject to design. The military and security domain, because of its existential importance to states, is one realm in which human enhancements are likely to be most enthusiastically adopted. For nations with powerful militaries, enhanced warriors may offer solutions to a number of current challenges, including the need for nations to project power without suffering casualties; a decline in birth rates among globally powerful states; and humans’ operational limitations in combat environments that feature accelerating velocities, volumes, and varieties of information. But warrior enhancements also have the potential to destabilize laws of armed conflict and related international norms; likewise, they present difficult challenges in the ethical, institutional, and operational realms. Ultimately, technological change puts the nature of human conflict into flux – as well as the nature of humanity itself.