This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book outlines that human presence on the planet looks today more troublesome than ever. In spite of countless warnings and interventions, ecological issues show few signs of overall improvement. United Nations Secretary-General Kofi Annan called for a Millennium Ecosystem Assessment, with the objective of evaluating the impact of ecosystem change on human well-being, as well as of developing a scientific basis for action. The book helps to understand this state of affairs and to assess the critical capacity of social theory in this regard. It is not about climate change or any other particular environmental issue. Data and discussions mentioned convey a sense of threat and preoccupation that most people share. The book attempts to shed light on cutting-edge social theorys opportunities and limitations for a critical engagement with the novel ways in which humans relationship with the biophysical world is conceived.