The focus of this book is on changes in the human situation wrought by unprecedented changes in science-based technology and expanding populations. Increasing scientific information concerning these changes and their consequences is beginning to alter people's perceptions, thus providing a rational basis for a worldwide environmental movement. This movement - complex and differentiated - works through political and educational means to establish new social priorities consistent with scientific findings and the sustainability of life on Earth. The success of this effort would signify a new phase of social development. The thesis of this book is that human-made changes in the condition of the Earth, accompanied by the changing attitudes and values implicit in the environmental movement, constitute an historical discontinuity. The present era represents a transition between the assumptions and conditions that have hitherto characterized the modern world, and those of the post-modern world that is emerging. Science and technology, so vividly symbolized in the view from outer space, are fundamentally changing our traditional beliefs about human opportunities and limitations - and these changes are slowly being reflected in international policies and laws. If humanity today succeeds in establishing a sustainable relationship to Earth, a higher level of civilisation will have been achieved. This thought-provoking view will interest students and professionals in the science and politics of the environment.