As a philosopher who has written on the subject of endangered species policy, I am asked from time to time to join a panel discussion on “the value of biological diversity.” Consider a representative example: At the National Forum on Biodiversity, a 1986 conference organized by the Smithsonian Institution and the National Academy of Sciences, I shared the platform with three resource economists and one ecologist. Everyone on the platform agreed that biological diversity has great value; the discussion focused on the question, can that value be quantified in dollar terms? I quickly perceived that I was in the middle of a polarized situation. The economists were there to demonstrate the efficacy of their methods for representing the value of wild species as dollars; the ecologist scoffed at these attempts as irrelevant at best and, at worst, as a symptom of moral depravity. Hovering in the background of discussions like this are celebrated examples such as that of the snaildarter and the Tellico Dam. In that case, the Supreme Court halted work on an almost-completed dam because it would have flooded the only known habitat of the snaildarter, a three-inch member of the perch family. The politically tortured case of the tiny snaildarter illustrates the dilemma environmentalists face in defending biological resources. Environmentalists initially opposed the Tennesee Valley Authority’s plans to dam one of the last free-flowing stretches of the Little Tennessee River because it would destroy white-water canoeing, flood natural ecological systems, and destroy anthropologically important Indian burial sites. Environmentalists made little headway, initially, as the bureaucratic processes ground forward and construction of the dam was begun. Then, in early 1976, in a dramatic development, biologists discovered a hitherto unknown species, the snaildarter, living in the waters upstream from the dam. Since the snaildarter spawned in shallow, fast-moving waters, the dam threatened to wipe out a distinctive form of life. Environmental economists, anxious to use their quantificational tools, saw the Tellico Dam as a case in which assigning a dollar value to a threatened species might tip the scales in an aggregation of costs and benefits of proposed projects.