The common agricultural policy started a continuous process of reforms including the decoupling of aids, proposed by the Luxembourg agreement, which constitutes an important stage. Based on modelling, the GENEDEC programme contributes to the assessments of the reform’s impacts as far as gross margins, land allocation, factors’ opportunity costs, and some environmental criteria are concerned. This paper recalls some of the results we obtained thanks to the AROPAj model of the research unit “Economie Publique” from Grignon (France).