In the environmental literature, accounts of cooperative progress commonly emphasize the activity and leadership of nongovernmental organizations, as well as the constitutive roles that environmental regimes play by legitimizing, by promoting reflectivist discourse, and by redefining roles. This essay lays out the differences between the constructivist and political-economic theories of environmental regime effectiveness and examines the extent to which the constructivist emphasis is empirically justified by three recent collections of case studies. Of the surprisingly modest effects that environmental regimes have had, most appear to have come through the use of mechanisms that already play a prominent role in the political economy literature. Constructivist processes, despite the attention they have received, appear to have had only a marginal impact.