Sustainability is the paradigm of our time, yet its use as a guide to planning or decision making is clouded by its ambiguity and the multiplicity of definitions in use. In this paper we address the issue of how best to deal with the multi-faceted nature of sustainability. We outline each of the facets of sustainability that have been discussed in the literature, but suggest that most of them boil down to three basic concepts: environmental stability, intergenerational equity and economic efficiency. Nevertheless, it remains difficult to link the concept to practical actions and decisions. We argue that a multiple criteria decision making approach is the best solution to this problem. This is consistent with the use of "sustainability indicators," but such indicators need to be selected carefully to be relevant to the essential elements of sustainability.