As the UNCED process draws global attention to the potentially enormous welfare implications of biodiversity loss, it is useful to take stock of what is and is not known about the problem. Combining the insights from the disciplines of economics and ecology, this paper outlines the most urgent questions for research in the area. Regarding humans less as managers than as co-actors with other species in complex self-organizing systems, we focus on the sustainability of resource use. In the context of biological conservation this implies the maintenance of sufficient biodiversity to assure the resilience of ecosystems delivering ecological services of fundamental value to human societies. The paper identifies four sets of research issues: the first comprises a set of ecological questions about the nature, measurement and con-sequences of change in biological diversity, both globally and at the level of particular ecosystems. The second concerns the economic valuation of ecological services as a means of judging the economic significance of biodiversity loss. The third concerns the driving forces behind biodiversity loss. It deals with both the proximate and underlying causes of change in the level of biodiversity. The fourth concerns the scope for changing the human behavior which threatens biodiversity, whether through the destruction of habitat, through specialization in production, or through harvesting strategies. The nature of the linkage between ecological and economic systems is discussed in the context of informational, institutional, ethical and cultural conditions. The paper takes a systems perspective emphasizing the importance of an interdisciplinary approach to biodiversity, and the gains from collaborative research.