This chapter opens with an account of commensurability and the assumption of mainstream economists that money can serve as a universal measure for valuation. It considers meaning of value monism and value pluralism and their relationship to commensurability. The chapter outlines the central problems with the mainstream economists' approach and considers alternative approaches to environmental decision-making. The view that rational decision-making requires a single measure of the value of different options has its basis in the utilitarian background to welfare economics. The classical utilitarian approach to ethics argues that the right action is that which maximises the welfare of affected agents. The chapter presents two grounds for criticism of the trade-off position. First, there are arguments specifically against monetary commensurability—the claim that money could offer a universal currency for measuring losses and gains across different dimensions of value. Second, there are reasons for suggesting that the very concept of a trade-off in values might be mistaken.