The objective of this research project is to evaluate the effect of agricultural policies on agriculture and the environment by using natural experiments. It has five parts. The first part focuses on the effect of land consolidation on the structural transformation of French agriculture. The second part focuses on the effect of Agro-Environmental Measures (MAE) on farmers’ practices. The third part looks at the motivations of conversion to organic farming. The fourth part aims to assess the effect of the de-densification of agriculture on the environment by measuring the effect of four major eco-conditionality measures: the introduction of compulsory fallow in 1992, the introduction of the mandatory grass strips in 2001, the building plan in 2005, which was accompanied by the obligation of better management of livestock effluents, and the conversion to organic farming. The fifth part focuses on the effect of agricultural advice on farmers’ practices.