This article analyses the role played by social norms in farmers’ decisions to enroll into an agri-environmental scheme (AES). First, it develops a simple theoretical model highlighting the interplay of descriptive and injunctive norms in farmers’ utility functions. Second, an empirical valuation of the effect of social norms is provided based on the results of a stated preference survey conducted with 98 wine-growers in the South of France. Proxies are proposed to capture and measure the weight of social norms in farmers’ decision to sign an agri-environmental contract. Our empirical results indicate that the injunctive norm seems to play a stronger role than the descriptive norm.