Focusing on the colonial and military context of ecosystems ecology, this chapter examines radioecology alongside nuclear testing in the Marshall Islands and Puerto Rico. The US Atomic Energy Commission funded ecological research to understand how radioactive pollution impacts environments and people. During this time, the “new ecology” became enfolded in the politics of militarized nuclear colonialism. The legacy of radioecology research persists in influencing ecological science today, shaping narratives of environmental management, resilience, disturbance and restoration ecology, and risk communication.