The regulation of financial markets and companies in Europe has undergone significant changes over the last decade. The Commission, Member States, and Parliament constructed regimes that facilitate new legislation, sanction delegation to the Commission for financial market law, and structurethe cross-border regulation of companies within the single market. The substance of this book is about that regime development.In creating the regimes discussed in this book, EU leaders contributed to the ongoing constitutionalisation of Europe by contesting and constructing norms. Each of the regimes required an explicit definition of the vertical relationship between the EU and the member states, and of the horizontalrelationship amongst the member states. It defined the kind of regulatory state that would be required, the mix of European and national bodies involved, and the procedures they were to follow in carrying out their functions. It also defined what kinds of national variation in related economic andsocial policy would be regarded as legitimate. As they made these agreements, European leaders simultaneously articulated what it meant to be a member state in the single market, and what it meant to delegate responsibilities to the EU. This constitutionalised these ideals by sorting out the issuesof EU and national responsibilities in a powerfully authoritative way. The theory of this book is about demonstrating the normative foundations of these constitutional agreements and showing how they had to be built on the shoulders of national ones.