The planet earth is non-growing in its physical quantitative dimensions, but of course it evolves and changes qualitatively. Likewise the economic subsystem, as its scale approaches that of the containing ecosystem, must cease physical growth, although qualitative evolution continues. The path of progress must shift from quantitative growth to qualitative development, if it is to be sustainable. Sustianable development is, therefore, qualitative improvement without quantitative growth beyond the assimilative and regenerative capacities of the ecosystem.