What potential problems does biodiversity loss create for humankind? What basis is there for biologists' concern about what has been described as the sixth mass extinction on our planet? The Biodiversity Programme of the Royal Swedish Academy of Sciences' Beijer Institute brought together eminent economists and ecologists to consider these and other questions about the nature and significance of the problem of biodiversity loss. This volume reports key findings from that programme. In encouraging collaborative interdisciplinary work between the closely related disciplines of economics and ecology, programme participants hoped to shed new light on the concept of diversity, the implications of biological diversity for the functioning of ecosystems, the driving forces behind biodiversity loss, and the options for promoting biodiversity conservation. The results of the programme are surprising. They indicate that the main costs of biodiversity loss may not be the loss of genetic material, but the loss of ecosystem resilience and the insurance it provides against the uncertain environmental effects of economic and population growth. Because this is as much a local as a global problem, biodiversity conservation offers both local and global benefits. Since the causes of biodiversity loss lie in the incentives to local users, that is where reform must begin if the problem is to be tackled successfully.