Human-induced environmental change is to be found throughout the world, but there are areas which scientists consider to be "critical regions" - regions that are particularly vulnerable to or suffering from environmental degradation. In this volume nine such regions are examined as case studies. In chapter one the authors provide a detailed look into the concepts of environmental criticality and endangerment, and propose formal definitions. The regional studies that follow serve to translate the conceptual framework into the physical and social realities of each area.