The Capital Markets Union (CMU) is a long-term and ambitious policy initiative of the European Union, which was officially launched in September 2015 with the adoption of an Action Plan by the Commission. Its strategic goal is to create a more diversified and integrated financial system by strengthening the capital markets in all Member States while deepening the level of their integration. In turn, this is expected to improve access to finance for businesses, provide more risk diversification opportunities for investors and contribute to the EU’s efforts to enhance economic growth and financial stability. Putting a fully-fledged CMU into place is not an easy task though. Rather, it requires several legislative and non-legislative measures which should collectively remove existing barriers to the efficient functioning and integration of EU capital markets. Among these actions, this thesis focuses on those legal interventions which aim to modernise the rules that govern the functioning of European primary markets as well as the activities that take place within them. These include, in particular, the introduction of a new, harmonised and highly sophisticated prospectus regime, as well as the creation of a pan-European regulatory framework on crowdfunding. Given that these measures are at the heart of the efforts to complete the CMU, the question arises as to whether and to what extent they are well-placed to achieve that. In answering the research question, the thesis proceeds as follows. Chapter 1 provides a systematic analysis of the underlying concept, assumptions and objectives of the CMU initiative. In this framework, it is claimed that, despite the use of the term ‘Union’, the idea of differentiation is another prominent feature of the CMU. This is clearly observed in the design of the reform agenda, which is shaped by the diverse and, at times, conflicting interests, preferences and needs of both the Member States and the various actors involved. Based on this, chapter 2 then defines a normative framework for the regulation of primary markets within the CMU. By so doing, it lays down a yardstick against which to measure the success of the regulatory actions taken in this area. After offering a brief overview of the theoretical underpinnings and evolution of the EU prospectus regime, chapter 3 turns to the new Prospectus Regulation, analysing the main reforms introduced there and evaluating their ability to contribute towards the development and integration of EU primary markets. Chapter 4 gives a detailed description of the ECSP Regulation and explores the extent to which it contributes to the completion of the CMU. The concluding chapter summarises the results and findings of the research.