The four major countries of East Asia—China, Japan, South Korea, and Taiwan—form one of the most densely populated regions on earth, and through the course of the late 20th and early 21st centuries the region experienced some of its fastest economic growth, propelled by the policies of state-led developmentalism. As a result of this density and these policies, the four countries in turn became some of the most environmentally degraded. As each achieved middle-to-high income status, however, the populace and then the regime in each country realized that they could not sustain either rapid economic growth or popular legitimacy without addressing the environmental consequences of this fast growth. The four states thus changed their fundamental economic policies from pure developmentalism to what we call eco-developmentalism, an attempt to reconcile economic prosperity with environmental sustainability. Although success so far has been mixed, this turn to eco-developmentalism has allowed these states to claim world leadership in mitigating environmental degradation.