The Role of Data in Capital Market Integration: Beyond Top-Down Legal Harmonization

European capital market integration has long been pursued through legislative harmonisation and supervisory convergence, most recently under the Capital Markets Union (CMU) and the emerging Savings and Investments Union (SIU). Yet, despite extensive regulatory efforts, significant barriers to cross-border investment and financial services persist, leaving the EU financial system fragmented along national lines. This paper argues that the governance of financial data is emerging as a crucial—yet underexplored—driver of market integration that complements traditional top-down legal harmonisation. The paper shows that recent EU initiatives increasingly rely on the creation of structured data ecosystems, or “data spaces”, designed to enhance the availability, interoperability, and machine-readability of financial information. By reducing search costs, improving comparability of financial products, and enabling data-driven supervision, these initiatives can facilitate cross-border transactions and foster more integrated market practices. Through a functional analysis of issuer disclosure, securities market infrastructures, and investment services, the paper demonstrates how data standardisation and information-sharing mechanisms—such as the European Single Access Point (ESAP), the proposed Regulation on Financial Data Access (FIDA), and other digital finance initiatives—may support both regulatory convergence and market-led integration. The paper concludes that effective data governance is becoming a key institutional complement to the EU’s traditional legal harmonisation strategy in the pursuit of integrated capital markets.