This essay reviews Jane Jacobs’s three major books: The Death and Life of Great American Cities,Cities and the Wealth of Nations, and The Nature of Economies. It traces her development of a hierarchy of places from neighborhoods to city regions to nations and the earth. All her places are defined by their predominant social activities, not by geographical boundaries. The themes of diversity, experimentation, adaptability, and democracy inform all her writings and form the basis of her moral analysis. Jacobs’s methods are contrasted to those of Lewis Mumford and the similarities of their moral concerns noted. Her latest book, a review of the basic hypotheses of ecology, successfully presents the idea that through self-correction, differentiation, and diversification, humans and their fellow organisms can best find sustainability.