As the basis for exploring the sustainability movement in a variety of environmental arenas and places across the United States, Mazmanian and Kraft develop in this opening chapter of their book a framework that locates sustainability - historically and conceptually - as the third epoch in the modern environmental movement. Following on the regulatory and market-based epochs, sustainability can best be understood as an effort to address in a more comprehensive manner the interdependence of natural and human systems, and address the threat to the former by the latter. The three epochs are compared along a series of dimensions for problem identification, implementation philosophy, policy tools, information and data management needs, and triggering events