This study is the result of several collective and individual research works on the connections between law, agriculture and the environment. Real but seldom highlighted, the impact of legal rules on determining farming practices shows an instrumentalised law which has gradually opened up to take into account the diversity and complexity, the interests and stakes in the implementation of sustainable agriculture models. We propose a number of factors for understanding the role of European and French law in the development of contemporary agriculture. Initially, the law was undoubtedly a tool that served the conventional technical and economic model. Then, when the context changed, its less obvious role was (and, above all, will be) to favour the implementation of sustainable farming practices.