The Environmental Sustainability Index (ESI) has been proposed by collaboration of the World Economic Forum, Geneva, Center for International Earth Science Information Network, Columbia University, and Yale Center for Environmental Law and Policy, New Haven as a measure of the overall state of the environment. This paper argues that the basic design of the ESI leaves much to be desired. It has conceptual problems in its visualization of environmental degradation and sustainability. The choice of variables as well as the statistical methodology of compiling the index is also found to be wanting. The paper then proposes an alternative methodology using Principal Components Analysis and argues that this is an improvement upon the ESI methodology. Given the likely use of aggregate environmental indexes in future environmental management, the critique advanced in this paper is of considerable significance.