In this paper my focus has been mainly on constitutional law in its cross-boundary concept and its relationship with that of national constitutions as how the constitutions of the nation-states are affected by the more comprehensive international and supranational treaties. I deal with the concepts of democracy, globalization, regimes collision, as well as international fragmentation of law in which constitutionalism plays a key role in trying to connect the different regimes. The other approach, of course, would be legal pluralism accepting the different regimes. The pivotal question would be how far constitutionalism has been successful in its global context; the obstacles and achievements. And, can EU be considered a successful constitutional framework as a regional and supranational institution? This thesis is trying to show the achievements of constitutionalism in a global context while urging for further cooperation in this regard in a global level.