Social movement theory has recently paid a lot of attention to the diversity of strategies used by social movements to pressurize companies, and has spawned an abundant literature on the combined perspective of social movement studies and market organization studies. This paper adopts a rather different perspective, drawing on market theories from the economic sociology of evaluation to assess a specific strategy developed by a number of groups within the environmental social movement, which relies on the market’s capacity to mediate their claims. The literature has widely considered why some environmental social movement organizations (SMOs) choose to address consumers, even though it is not in their tradition to do so and even though their objective is not directly related to consumption issues. I seek to contribute to this debate by analysing the ‘how’ rather than the ‘why’, by highlighting a specific social movement strategy which is mediated by market mechanisms. The paper provides an in-depth analysis of a strategy consisting of attempts to change the most prevalent valuation criteria within the market by introducing principles of worth that rely on products’ environmental performance. This involves activist organizations suggesting new product valuation criteria, and then seeking to convince firms that consumers’ preferences are changing.Their assumption is that firms will see new business opportunities, which will prompt them to adopt more eco-friendly practices. This market mediation strategy is designed to encourage firms to shift towards more eco-friendly supply practices, by creating business opportunities for them. It shows how SMOs, in order to directly shape consumers’ preferences, urge them to introduce eco-friendly principles of worth into their valuation of products by providing them with market devices to help in their purchasing choices. By applying these strategies, SMOs seek to shape the market and create business opportunities for firms. Their intention is to make companies see the value of changing some of their practices by introducing new eco-friendly features in their products, because consumers have been convinced by SMOs of the value of such features. SMOs must then pursue two important objectives: one is to shape consumers’ preferences for that kind of valuation category on the market by convincing them of their responsibilities and their role as agents of change; and the other is to convince companies that a real shift in consumers’ preferences is taking place in the market, so that they see it as an interesting opportunity to benefit from the SMOs’ shaping of the market.