In recent years, there have been numerous academic and policy debates on the delivery mechanisms of European Union (EU) funds in member states. Studies focused on issues arising, for instance, during the management and implementation of EU aid at the local level but devoted less attention to the economic and institutional impact of EU funds. To what extent do EU funds act as drivers of socio-economic development and institutional change? Theoretically, this paper contributes to debates about economic convergence and the institutional spillover effects generated by EU aid across national and local settings. Empirically, the paper evaluates the impact of EU aid in Bulgaria and Romania after a decade of EU membership. Firstly, the paper examines a mix of quantitative indicators and secondary sources on the socioeconomic impact of EU funds in the two countries. Secondly, using original qualitative evidence, the paper assesses the spillover effects of EU aid on domestic institutions and stakeholders, policies and practices. Finally, the paper provides an analysis of the unintended domestic consequences triggered by EU funds. It contributes to growing debates on the impact of European aid and suggests potential avenues for policy development and for further academic research in this area.