A new report issued jointly by the Atlantic Council and the Stimson Center, The Security of Cities: Ecology and Conflict on an Urbanizing Planet, argues that the environmental security field has yet to incorporate global urbanization, the twenty-first century’s central demographic trend, fully into its purview. Environmental security, which focuses mainly on conflict arising from resource scarcity, control over natural resources, and environmental degradation, historically has focused much attention on the rural poor in the developing world. Yet the rural poor are neither the primary cause of rising global demand for natural resources nor of environmental degradation. The culprits are people who live in cities. The collective behavior of billions of urbanites is the main reason why fossil fuels are mined from the ground, coastal mangroves are turned into fish farms, and the Earth’s atmosphere is changing.