The constitutional law of the European Union(EU) is a chameleon. It changes its skin according to the viewpoint of the observer. How we understand it depends on our standpoint and purpose. Of course this is inevitable in the study of any social science, including law. In the case of the EU, its specific character makes unusually complicated any enquiry to understand its constitution. First of all, the purpose of this article is to elaborate a conceptual framework of EU constitutional law. To clear the conceptual ground, we must define what we mean by constitution in the EU. On the basis of setting up the definition of EU constitutional law, this study tries to figure out how the Community has developed and systematized its constitutional law over the last five decades. A third, more political, purpose is to find out what the roles of EU constitutional law are in the process of European integration. A final purpose is to develop the study of EC law in the political, economic. and socio-cultural contexts of the European Union. To sum up, the founding Treaties of the European Communities and their amendments, like national constitutions, serve as the highest norm in the Community legal system, define the conditions for the exercise of political power of the Community institutions, and confer upon EU citizens the power to assert their rights against the supranational organization, that is, the Union.