ABSTRACT
Sustainability is now becoming a key word for every policy concerning development, economics, ecology, and social issues. However, we sometimes get the feeling that sustainability is used as a black box with very different meanings. In this chapter we will try to shed some light on this notion. The first section points out some general features that we believe are implicit in the definition of sustainability given in the Brundtland Report (WCED 1987). The second section develops the various relationships that one finds between the economy and the physical and biological environment There we stress the necessity to guarantee the physical viability of the system before starting any discussion on sustainability. The third section attempts to provide some measurable physical indicators of survivability. The fourth section presents some enlarged neoclassical models of sustainability, but we point out that more short-term available indicators are needed. The fifth, and final, section contains concluding remarks and qualifications.
