The EPI centers on two broad environmental protection objectives: 1) reducing environmental stresses on human health and 2) protecting ecosystem vitality. Environmental health and ecosystem vitality are gauged using sixteen indicators tracked in six established policy categories: Environmental Health, Air Quality, Water Resources, Biodiversity and Habitat, Productive Natural Resources, and Sustainable Energy. The EPI complements a separate index, the 2005 Environmental Sustainability Index (ESI). The ESI is a gauge of a country's long-term environmental trajectory, whereas the EPI focuses on a country's current environmental performance. For more on the two indexes, see the complete literature on the EPI and the ESI at www.yale.edu/epi/ .