Arguably, no curve in the world increases indefinitely--- certainly no growth curve of human society. The quest for sustainable use of the planet involves estimating levels of activity, particularly resource use, that can continue indefinitely. Since the biosphere is dynamic, this continuation is not a stagnant, steady-state situation but rather a mutualistic interactive relationship between human society and the planet's ecological life support system. Human technology, creativity, and ingenuity may modify natural laws, but cannot be used to repeal them. Attempts to maintain the recent exponential growth of the human population, affluence, and artifacts cannot continue forever, or probably even for another century. At best, quality of life will be diminished, and, at worst, a substantial loss of human life will occur if both ethical and ecological issues are not freely and openly discuessed. Sustainability may be visionary and unattainable, but it does offer an opportunity to improve the quality of life for futrure generations of humans and other life forms, an opportunity that is far greater than possible with present unsustainable practices.