The regulatory boom in EU securities law, induced by the Financial Services Action Plan (FSAP) and the Lamfalussy-process of multi-level regulation has seen the emergence of a comprehensive body of law in the field of investor protection rules, notably under the form of information disclosure (Prospectus and Transparency Directives, Market Abuse Directive) for issuers and conduct of business rules for investment firms and credit institutions. It is often claimed that the European directives are based on the paradigm of maximum harmonisation, thus creating a common law (ius commune) in the field of investor protection in Europe. In this paper, we raise some questions as to this proposition, stressing the need to distinguish between the level (maximum or not) and the substantive scope (what has been harmonised?) of harmonisation. Furthermore, we submit that both the continued fragmentation regarding supervision of the harmonised standards, notably in the field of conduct of business rules, and the absence of common rules on private enforcement through civil liability may generate disincentives for different actors to adequately take advantage of the potential benefits of market integration.