The paper analyzes the impact of the modern 'nomofilachia' of the Italian Court of Cassation above the institutions of Private Law. Court's application of domestic rules in the field of Private Law (so called 'diritto vivente') is in fact based on a coordinated interpretation of the Italian Consitution and Law with the European rules and principles within a complex legal system made of national and international sources. So that the current model of 'nomofilachia' (article 65 ord. giud.) is inspired by a new idea of legal certainty. This certainty is no more absolute but only 'relative' and 'open-ended' because of the attitude of the Italian Courts (and of the same Court of Cassation) to make the national rights and the constitutional principles conform to the Treaty of Lisbon and to the Charter of Nice, in a context of common European Law. Significantly the activity of the Italian Court of Cassation has gradually covered the whole subject of social citizenship, labor rights, the relations of the individual with the State and the rights of individuals.