It is a great pleasure to introduce this volume edited by Elias Mossialos, Govin Permanand, Rita Baeten and Tamara Hervey. It is a volume which continues the success of two earlier books commissioned by the Belgian government and published by Peter Lang Publishing Group in 2002.1 The topic of this contribution is a crucial one. Indeed, one can hardly imagine a subject closer to the lives of European Union (EU) citizens than an exploration of how EU law and policy has influenced, and will continue to influence, the health systems of the 27 Member States. This two-dimensional perspective means that this work will certainly be studied with great interest by all concerned with the functioning of the EU as well as by those wanting to discover more about national health systems. In principle, in light of Article 152 of the EC Treaty, national authorities are solely responsible for health care. Yet, though the Member States are free to decide how to deliver and organize health services, they must do so in compliance with other aspects of the Treaty, in particular with the fundamental freedoms and elements of competition law. Put differently, national health systems are not enclaves of national sovereignty insulated from European market integration. While EU legislators may not regulate health care as a means of promoting social cohesion, they may, however, enact legislation relating to those aspects affecting the establishment and functioning of the internal market. Given that national health systems are deeply rooted in social solidarity and welfare, the “constitutional asymmetry” (to borrow the term used by Fritz Scharpf) laid down in the Treaty gives rise to important tensions.