The legislative dynamic in the post-Amsterdam era is increasingly challenging the Schengen Acquis as it leads to both legal harmonization and fragmentation. SIS, EURODAC, Prüm and, more recently, VIS have changed Europe's law enforcement authorities considerably. However, it is questionable whether the fragmented legal harmonization can provide sufficient compensatory measures in light of the increasing international criminal links and illicit migration within the Schengen countries. This analysis focuses on the theoretical considerations regarding the various concepts of Europeanization, and on their effect on the multi-layered policy processes and actors implementing the Schengen complexes. This work is directed at students, researchers and practitioners wishing to survey the current legal situation. The legislative dynamic in post-Amsterdam era is increasingly challenging the Schengen Acquis as it leads to legal harmonization and fragmentation. This book focuses on theoretical considerations regarding various concepts of Europeanization, and on their effect on the multi-layered policy processes and actors implementing the Schengen complexes.