The enlargement of the EU has highlighted the challenges of compliance, but it has also helped to suggest new compliance methodologies. The combination of methodologies used by the EU and the differing levels of enforcement available are characteristic of the EU's compliance system, permitting the remarkable reach and penetration of EU norms into national systems. In this new study six authors offer their 1ssessment of the enforcement procedures and compliance processes that have been developed to ensure Member State compliance with EU law. The first three chapters examine the merits of combining both coercive and problem-solving strategies, describing the systems in place and focussing on the different levels at which compliance mechanisms operate: national, regional, and international. It also looks at horizontal compliance as well as 'from above' compliance, creating a complex and rich picture of the EU's system. The final three chapters of the book focus on different aspects of compliance seen from a national perspective. The first analyses the two bases for the use of criminal sanctions to enforce EU law: the ability of Member States to choose to include criminal penalties for non-compliance in their national law; and the imposition of criminal sanctions at a national level by EU law itself. The book then moves on to a discussion of the role of national courts in ensuring Member State compliance with, and enforcement of, EU law. It examines the role of national constitutional courts in facilitating compliance with EU law and draws comparisons between EU law and international law and their interactions both with each other and with national constitutional courts.