Since the end of the Cold War, many policymakers and researchers have been rethinking and pushing the boundaries of the definition of security. Perhaps the most extensive and controversial part of this project has been the numerous and varied attempts to identify links among environmental change, conflict, and security. But concern has recently been raised about whether a decade of environmental security research, debate, and policy experimentation has produced worthwhile results. This article argues that such concern is premature. Environmental security has (a) reinvigorated important elements of security research and policy; (b) made pioneering contributions to understanding the shifting sources of global violence and the changing requirements of security; (c) contributed to a broader debate about the social and political effects of transnational change; and (d) been a conceptual and political boon for the environmental movement. Now is the time to build on these gains instead of abandoning them.