While acknowledging the need for "sustainability", this paper summarizes the problems that have been encountered in our understanding and use of this concept. It explores the efforts of others to define the concept within the context of specific disciplinary areas and sets forth a proposal for a basic understanding of the term "environmental sustainability" as an expansion of our common perception of the nature of human activity so as to more clearly connect it with the ecological concept of interdependence and to serve as a goal for environmental managers. Keywords: Defining Sustainability, Ecological Services, Environmental Sustainability, Goals of the Environmental Professional, Principles of Environmental Sustainability.