Limitation of sovereignty by European integration is a key issue of contemporary law in Europe. This book collects the perspectives of researchers from various European countries on the topic. The constitutional orders of the Member States of the European Union are the basis for the integration process. The traditional sovereignty concept is in confl ict with the supranational power of the EU created according to the provisions of the national constitutions. This confl ict is refl ected by the debate on constitutional identity which seems to be the new version of a “supranationalised sovereignty”. Identity in this sense draws the borderline between national autonomy and supra-nationality. Integration must be based on an equilibrium of both. The introductory contribution ( Rainer Arnold ) explains, with the use of Germany as an example, how the Constitution enables the legislator to put into effect “open Statehood” and how the Constitutional Courts in Germany and other countries are trying to fi nd the above mentioned equilibrium. The concept of constitutional identity and the question of the competence to decide what it entails are of major importance. The jurisprudence of the French Conseil constitutionnel developing the criterion of the conditions essentielles d’exercise de la souveraineté as well as the rigid and questionable English doctrine of parliamentary sovereignty are taken into consideration. How European integration, which is characterized by the existence of various constitutional levels, affects the traditional doctrinal basics of Constitution-making and reforming power is dealt with in the refl ection of Francisco Balaguer . National and constitutional identity as an emerging key concept of integration is double-sided: a national and a supranational perspective has to be applied and adequately harmonized. Luca Mezzetti and Sinisa Rodin give an insight into the two approaches.