The city at its best is an eco-community. Urbanization is not only a social and cultural fact of historic proportions; it is a tremendous ecological fact as well. We must explore modern urbanization and its impact on the natural environment, as well as the changes urbanization has produced in our sensibility towards society and toward the natural world. If ecological thinking is to be relevant to the modern human condition, we need a social ecology of the city. This book attempts to lay the groundwork for such a social ecology. It tries to develop a concept of the city in those participatory terms that are uniquely characteristic of all ‘ecosystems’. It relates ecology’s participatory sensibility to the city in all its forms over the course of history, partly to show that the city was a social eco-community at various times insofar as it fostered diversity, mutualism, and connectedness. In applying a participatory sensibility to the city, I have been obliged to take the reader on a voyage into the evolution of the city. What I wish to do is redeem the city, to visualize it not as a threat to the environment but as uniquely human, ethical, and ecological community that often lived in balance with nature and created institutional forms that sharpened human awareness of their sense of natural history.