The economic literature on Agri-environmental Schemes (AES) largely considers that farmers participate in contracts if the payment offered is superior to their opportunity costs. Psychological and social forces may however be at play in this decision. This article analyses the role played by social norms in farmers’ decisions to enrol into AES. It develops a simple theoretical model highlighting the interplay of descriptive and injunctive norms in farmers’ utility functions. Results of this model lead us to propose few policy recommendations to counter or, in other contexts, to take advantage of the influence of social norms to increase farmers’ participation to AES.