The term biological diversity refers to the variety of life forms on Earth. It is the totality of the different forms of life and their interactions with each other and with the physical environment that has made the Earth habitable for human beings. Ecosystems provide what is essential for life, protect against natural disasters and diseases, and are the foundation of human cultures. The Millennium Ecosystem Assessment — a scientific undertaking involving more than 1,300 experts from 95 countries — recently confirmed the enormous contribution of ecosystems to human existence and well-being. And yet, even as we begin to understand what is at stake, genes, species, and habitats are rapidly disappearing.