Contrary to predictions by many experts, Ukraine’s military has been resilient in the face of the Russian government’s invasion. Drawing on the logic of polycentric defense, this article helps explain how Ukraine has remained resistant against a conventionally more powerful adversary. We argue that polycentric defense in Ukraine has four benefits that aid counteroffensive efforts against invasion. First, polycentric defense facilitates the use of local and context-specific knowledge. Second, it permits competition, experimentation, and flexibility. Third, it reduces single-point failure vulnerabilities. Fourth, it encourages a wide variety of individuals to join the armed forces and contribute to the war effort. We present evidence of the benefits of polycentric defense in the context of the ongoing war in Ukraine.