The environmental Kuznets curve (EKC) hypothesis proposes that there is an inverted U-shape relation between environmental degradation and income per capita. This has been taken to imply that economic growth will eventually redress the environmental impacts of the early stages of economic development. The literature on this issue has developed rapidly over the last few years. This paper examines whether progress has been made on both understanding the EKC phenomenon and on addressing the various criticisms raised against some of the empirical studies and their interpretation in the policy literature. Though basic EKC studies continue to be carried out, recent work has focused on the effect of a variety of conditioning variables on the environmental impact-GDP relationship. Some attempts have also been made to examine the history of the relationship in individual countries. The econometric techniques used have improved. However, empirical decompositions of the EKC into proximate or underlying causes are either limited in scope or non-systematic, and explicit testing of the various theoretical models has not yet been attempted.