The model and the ideological fundament of contemporary States are under the dynamic evolution. The doctrine of Nation-State proves to be precarious and inadequate toward the sociological reality which allow taking into account different cultural or ethnic groups that make part of the society. The relevance of the Nation, a political and legal creation that represents the unified and homogeneous social body on which is based the State, has become contingent.Contemporary States, being faced with the claims of ethnic or cultural groups, are forced to make changes in their legal and institutional systems. The principal rules of the Nation-State, based on the logic of universalism and individualism, such as the unity of the people, the sole official language, the equality of citizens before the law, the indivisibility of the public power and the administrative decentralization, are jeopardized by the claim of the right to be different, or even of the right to autonomy. The configuration of the logic of pluralism, which advocates legal recognition of the ethical or cultural differences between the members of the society, is the challenge. How can this new logic be introduced in a legal system that adheres to the opposite political ideas? Will this ideological mutation require the creation of a new State model? What are the basic elements of this novel form of State?The study on the evolution of the French, Belgian, Hungarian and Romanian legal systems with regard to the ethnic and cultural diversities, allows us to observe legal and institutional modifications of European countries according to different political and demotic structures. The transformation of the rules relating to the recognition of the people of State, on the one hand, and the consecration of the rules relating to the political formation of the ethnic groups, on the other hand, testify to the archaism of the model of the Nation-State. This observation leads to a new design of the Nation as the fundament of the political power which consists of ...