Among the less desirable results of human activity on this planet are thefollowing: pollution of atmosphere, rivers and oceans, land degradation, deforestation, elimination of species at an unprecedented rate, the build up of greenhouse gases, the depletion of the ozone layer. This list could easily be extended. It is generally assumed that the results are undesirable, that they result in the destruction of something with positive value. But what? What is the value of the natural environment that would be lost if the environment were destroyed or seriously degraded? This, essentially, is the central question of environmental ethics.