The Environmental Sustainability Index (ESI) is a composite index that tracks a diverse set of socio-economic, environmental, and institutional indicators that characterize and influence environmental sustainability at the national scale. It was launched in 1999 by Professor Daniel C. Esty, Director of the Yale Center for Environmental Law & Policy, in cooperation with Columbia University's Center for International Earth Science Information Network (CIESIN) and the World Economic Forum's Global Leaders for Tomorrow Environment Task Force.

The 2005 ESI report, published at the World Economic Forum’s Annual Meeting in Davos, Switzerland, ranks 146 countries with regard to the environmental sustainability of their past, current, and projected socio-economic and institutional development trajectories. The ESI has also helped to demonstrate new conceptual hypotheses concerning the drivers of successful environmental protection. These developments, in turn, make significant contributions to the abilities of countries to align their resources more effectively with identified priorities.