Before turning into its present form, this book has had many lives that span over almost a decade. Its origins can be traced back to many heated discussions over Europe’s polity and transnational fields within a small group of friends (Antonin Cohen, Mikael Madsen, Guillaume Sacriste) and, later, within a more formal research network named Polilexes (‘Politics of Legal Expertise in European Societies’) and financed by the French Agence nationale de la recherche. Throughout its development, the critical input that I received from Yves Dezalay and his tireless passion for transnational research have been widely inspirational. All these exchanges grew into an individual project parallel to the collective and collaborative one, on which I started working during my stay at the European University Institute in Florence as a Marie Curie fellow. There, I greatly benefited from the critical mass of EU scholarship and the interdisciplinary atmosphere that is so particular to that place. Many discussions and debates with wonderful scholars such as Bruno de Witte, Yves Mény, Christian Joerges, Karen Alter, Kiran Patel and Heike Schweitzer have helped me a lot. Eventually, the project was turned into an Habilitation à diriger des recherches that I presented at the Université Paris 1-Sorbonne in March 2010, with the support of Bastien François. Along the way, some early parts of this overall research were published in a variety of disciplinary fields including law (the European Law Journal and Law and Social Inquiry), sociology (the American Journal of Sociology and International Political Sociology) and political science (European Political Science Research, Revue française de science politique, etc.), and I am therefore indebted to my co-authors and co-editors (Bruno de Witte, Antonin Cohen, Didier Georgakakis, Mikael Madsen, Stephanie Mudge and Cécile Robert) as much as to various referees for pushing me forward