Many conservationists have become enamoured with mainstream economic concepts and approaches, described as pragmatic replacements for appeals to ethics and direct regulation. Trading biodiversity using offsets is part of the resulting push for market governance that is promoted as a more efficient means of Nature conservation. In critically evaluationg this position I start by explaining the assumptions behind biodiversity and ecosystem valuation and how economic logic legitimises, rather than prevents, ongoing habitat destruction and treats species extinction as optimal. Biodiversity offsets provide a means for operationalising trade-offs that are in the best interests of developers and make false claims to adding productive new economic activity. Contrary to the argument that economic logic frees conservation from ethics, I expose the ethical premises required for economists to justify public policy support for offsets. Finally, various issues in offset design are raised and placed in the context of a political struggle over the meaning of Nature. The overall message is that, if conservationists continue down the path of conceptualising the world as in mainstream economic textbooks they will be forced from one compromise to another, ultimately losing their ability to conserve or protect anything. They will also be abandoning the rich and meaningful human relationships with Nature that have been their raison d'être. (author's abstract) / Series: SRE - Discussion Papers