This paper critically evaluates the notion and application of economic, monetary valuation of biological diversity, or biodiversity. For this purpose four levels of diversity are considered: genes, species, ecosystems and functions. Different perspectives on biodiversity value can be characterized through a number of factors: instrumental vs. intrinsic values, local vs. global diversity, life diversity vs. biological resources, etc. A classification of biodiversity values is offered, based on a system of logical relationships among biodiversity, ecosystems, species and human welfare. Suggestions are made about which economic valuation methods can address which type of biodiversity value. The resulting framework is the starting point for a survey and evaluation of empirical studies at each of the four levels of diversity. The contingent valuation method is by far the most used method. An important reason is that the other valuation methods are unable to identify and measure passive or nonuse values of biodiversity. At first sight, the resulting monetary value estimates seem to give unequivocal support to the belief that biodiversity has a significant, positive social value. Nevertheless, most studies lack a uniform, clear perspective on biodiversity as a distinct concept from biological resources. In fact, the empirical literature fails to apply economic valuation to the entire range of biodiversity benefits. Therefore, available economic valuation estimates should generally be regarded as providing a very incomplete perspective on, and at best lower bounds, to the unknown value of biodiversity changes. © 2001 Elsevier Science B.V. All rights reserved.