In Chapters 2 and 3 we showed that cities have long confronted environmental issues such as pollution, disease and degradation. They have also responded to these problems with policies, pollution proclamations and other legislative efforts. However, the 1970s saw a profound transformation as concern for the environment became legitimized and institutionalized. Environmental protection and management is no longer on the margins, or occasionally dealt with by municipalities: it is now integrated into mainstream public consciousness and public policy. The subject matter of Chapters 10-16 is best understood within the context of the modern environmental movement. This chapter provides a brief overview of the movement as it applies largely to the US, although we draw on examples from other countries around the world.