Sustainability means that the current use of resources does not compromise the well-being of future generations. Ever since Malthus (1798) forecast that population tends to grow faster than the growth of resources to support the population, people have claimed that current resource use is unsustainable, so future generations will be materially worse off than those in the present, yet for more than two centuries this has not been the case. The reason is that markets, and market prices, act to conserve scarce resources, and in market economies, entrepreneurs have an incentive to discover more efficient ways to use resources. The claim that twenty-first century market economies are not sustainable is not supported by the evidence. This paper explains why entrepreneurship in market economies produces sustainable economic progress.