This book collects case studies on the state of the art of enforcement in multi-level regulatory systems, each addressing a different policy area. Multi-level regulatory systems are a phenomenon of post-modern society. They are complex legal systems, regulated by several levels of legislation (national, European/supranational, international), where national, supranational and international actors interact. Challenges in relation to enforcement are analysed in and across different legal disciplines and from a political science perspective, with a strong EU focus. The variety of case studies permits to draw conclusions on common conceptual challenges of multi-level enforcement systems and to suggest generally applicable solutions.With contributions byChrysa Alexandraki, Ioannis Asimakopoulos, Kelly Blount, Kei Hannah Brodersen, Giovanni Chiapponi, Nicole Citeroni, Simona Demková, Dimitrios Kafteranis, Katalin Ligeti, Pier Mario Lupinu, Branimir Stanimirov, Igor Tkalec, Carsten Ullrich and Panagiotis Zinonos.