The paper investigates the value of biodiversity as it relates to the productive value of services provided by an ecosystem. It analyzes how the value of an ecosystem can be "greater than the sum of its parts." First, it proposes a general measure of the value of biodiversity. Second, this measure is decomposed into four components, reflecting the role of complementarity, scale, convexity, and catalytic effects. This provides new information on the sources and determinants of biodiversity value. Third, the paper examines the role of uncertainty. In this context, the role of risk and of downside-risk exposure and their effects on the value of biodiversity are explored. This provides useful insights on how management and policy decisions can affect the value of biodiversity.