The paper investigates the concept of sustainable development from the neoclassical and ecological economics point of view. Different definitions of sustainability are considered and deep analysis is done in that area. Exactly what is it that is supposed to be sustained in “sustainable” development? Two broad answers have been given. First, utility should be sustained, say the neoclassical economists; that is, the utility of future generations is to be non-declining. The future should be at least as well off as the present in terms of its utility or happiness as experienced by itself. Second, physical throughput should be sustained say ecological economists. More exactly, the capacity of the ecosystem to sustain those flows is not to be run down. The future will be at least as well off as the present in terms of its access to biophysical resources and services supplied by the ecosystem. Author adopts the throughput definition and rejects the utility definition, for two reasons. First, utility is non-measurable. Second, and more importantly, even if utility were measurable it is still not something that we can bequeath to the future. Utility is an experience, not a thing. We cannot bequeath utility or happiness to future generations. We can leave them things, and to a lesser degree knowledge. Reducing poverty is indeed the basic goal of development, but it cannot be attained by growth for two reasons. First, because growth in GDP has begun to increase environmental and social costs faster than it increases production benefits. Such uneconomic growth makes us poorer, not richer.