The argument that environmental degradation will lead to conflict is a well established concern of international studies, and it dominates the literature on environmental security. This article critically examines theories about wars fought over scarce ‘environmental’ resources, ‘water wars’, and the argument that population growth may induce conflict. One significant research programme—the Project on Environment, Population and Security— is also discussed. The article ends with an evaluation of the theoretical merits and practical effects of the environment–conflict thesis. It argues that the environment–conflict thesis is theoretically rather than empirically driven, and is both a product and legitimation of the Northern security agenda.