In the early 1980s cultivated land planted with grain legumes increased very rapidly in Europe due to specific EU policy to support protein production (premiums, funding of research and extension programs). But with the evolution of the CAP (decoupling and reduction of subsidies per ha) and international commitments (Blair House agreement with consequence of duty-free soybeans importing) the surface area set aside for grain legumes declined substantially by 78% from 1993 to 2008. Recently, several EU regions announced new premiums to boost grain legume crops. This paper presents a study using a bio-economic model to assess impacts of the economic incentive measures in the Midi-Pyrenees region (France) on legume introduction in cropping systems by analyzing, at farm level, the farm income and total energy consumption.