Life on Earth is embarking on its sixth mass extinction. It is vital that the scientific and technical challenges raised by the current biodiversity crisis do not obscure the fundamental issues concerning the place of humanity within nature and man's responsibilities towards his environment. Unless the right questions have been posed from the beginning, the responses of ecologists, engineers and economists will be worthless. Far from being catastrophism or fatalism, the philosophical approach opens up inspiring horizons: an opportunity to reconsider the value of nature and the meaning of the common good, the possibility of developing more harmonious relationships between individuals, cultures and all life forms. This new edition integrates a number of recent developments in the field of nature conservation: the ever-expanding approach to ecosystem services in terms of monetary valuations and conservation tools based on market principles, as well as phenomena which justify a re-emphasis on the diverse fields where nature is valuable and the need for dialogues between them.