The destruction of natural habitats has prompted concerns about the loss of biological diversity. Regrettably, however, there is no consensus among either biologists or economists on the most meaningful measures of biodiversity. Fundamentally different definitions are useful in asking fundamentally different questions. Considerable attention has been given to the value of diversity in search models. A measure of “aggregate variability” is appropriate to such models. Values derived from search models tend to be well behaved; they exhibit diminishing returns in diversity. In contrast, a definition of diversity as “relative abundance” is more appropriate to more complex objective functions. Values derived in these models are not necessarily well behaved. The differences between diversity values arising in search models and those arising from more general objectives are demonstrated. An example shows that “consistency tests” applied to measures of valuation may not be useful when diversity per se is being valued.