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 five years. This paper examines whether progress has been made on both understanding the EKC phenomenon and on addressing the criticisms raised against the early studies.