This book examines ecosystems and the biodiversity they embody which constitute "environmental capital" on which society depends in multifaceted ways. The "ecosystem services" that flow from this capital including formation of soil and renewal of its fertility, management of flows of fresh water, maintenance of the composition of the atmosphere, pollination of flowers and crops, control of the distribution and abundance of pests and pathogens, production of fish and game in unmanaged and lightly managed ecosystems, aesthetic and recreational values from pristine landscapes, maintenance of the "genetic library" of global biodiversity as a source of future insights and innovations benefiting humankind, and important contributions to keeping climatic conditions in the range to which human society and current ecosystems are adapted. It has become clear, however, that biodiversity and other important components of the environmental capital producing these services are being degraded by human activities, and that the degradation of this capital has already impaired some of the associated services, with significant adverse impacts on society.