This book provides an in-depth guide to researchers and practitioners who are interested in analysing the evolution of EU law from a national and comparative constitutional law perspective. The volume deals with questions of how EU member states’ constitutional systems, including the subnational tier, interact with the supranational level. It maps the evolution over time of constitutional strategies in the face of multi-level governance and individual contextual factors on an empirical basis. The volume comprises 12 national reports written by leading experts in constitutional and EU law, and in political science. The countries discussed include the six founding member states, together with a selection of member states in which a clear-cut evolution in the national constitutional approach towards the EU can be observed. These comprise the Czech Republic, Denmark, Hungary, Poland, Portugal, and the United Kingdom. The latter is included as an “extreme” case in which the change in constitutional strategy over time has resulted in withdrawing from the Union altogether. Taken together, the book assembles the building blocks of an explanatory theory of constitutional strategies in the face of multi-level governance. The volume will be of interest to students and researchers in comparative constitutional law, political science, and multidisciplinary EU studies. It will also be a valuable resource for policy-makers.