This article proposes an analytical framework and method for measuring transaction costs associated with the application of French agri-environmental policies. Transaction cost theory attempts to take into consideration the effect of costs involved in drawing up and securing contracts for ecc organization and efficiency. Originally developed to understand forms of industrial organization, it has proven relevant in the assessment of public policies, in particular territorial and environmental policies involving a large number of players, often with diverging interests, which raises important issues of information asymmetry. The proposed method is applied to two highly different initiatives, one fairly standard («grass premium») and the other localized («local farming contract»). The diverse forms transaction costs may take for the various players involved (government departments, professional organizations, farmers) are shown, as is the usefulness of analysing these costs for an accurate evaluation of the effectiveness of the policies.