Italy and Spain throughout history have hosted in their territories different political, social, economic and cultural realities. This aspect determined the course of their territorial organization at the time when their democratic states were created. Thus, both in Spain and in Italy, at the end of their periods of dictatorship, and as a result of consensus and agreement among different groups, a compound regional State was chosen. In both countries, this decision represents an intermediate position between a separatist federalist tendency and a centralist one. Likewise, neither constitutions clearly defined the existence of a regional state. However, the joint interpretation of the principles of unity and autonomy contained in both texts and the later judicial pronouncements of the Constitutional Court, lead to the development of a clearer interpretation of these models of territorial organization. The Italian Regional State has developed much more slowly than the Spanish State of Autonomous Communities. This has happened because the evolution of the Spanish Regional State has been closely linked to the demands of Catalan and Basque nationalism while the evolution of the Italian Regional State has been more closely linked to satisfying, especially the economic interests of the northern regions. Thus, even though the administrative and political organizations of the Spanish State are very similar to those of the Italian State, the Spanish State has achieved a greater degree of decentralization.