Sustainable development has become a primary objective for many countries throughout the world since the late 1980s. A major difficulty associated with sustainable development objectives, however, is the absence of reliable indicators to measure progress towards the goal of sustainability. The 'ecological footprint' provides an estimate of the land area necessary to sustain current levels of resource consumption for a given population. On an aggregate basis, the ecological footprint may be compared with the amount of ecologically productive land available to give an indication of whether consumption patterns are likely to be sustainable. This paper proposes the use of a modified form of input-output analysis to calculate the ecological footprint. The input -output approach provides a consistent means of calculating an ecological footprint using data collected as part of the system of national accounts in most developed countries. In addition, it makes explicit the link between the level of economic activity in a country and its corresponding impact on the environment. An application of this methodology to New Zealand indicates that it takes 3.49 has of ecologically productive land per year to sustain the average New Zealander's current level of consumption.