The Treaty of Amsterdam has introduced important changes into the constitution of the European Union, for example, in the fields of internal and external affairs and employment policy, which will impact upon the future of the Union. Also of considerable importance is the new option to establish closer co-operation between a group of Member States, as well as certain institutional modifications. Particular attention is paid to areas of the Treaty of Amsterdam which are unclear or apparently deficient. All of these topics are of greatest importance within the course of the ongoing thematic debate, not the least on future EU-enlargement. The book is addressed to experts and anyone interested in European affairs.