This dissertation evaluates the effectiveness of the EU in promoting lasting liberalizing reforms in Central and Eastern Europe (CEE) before and after accession. It focuses on an area of governance with deep implications for both the quality of democracy and the prospect of economic development in the region - corruption control. The major finding is that since enlargement the EU has not had such strong direct and far-reaching effects as it did before accession. In analyzing corruption control both as a dependent variable as well as an independent one affecting FDI, I make three claims and substantiate each using a mixed-method approach featuring both time-series analyses and qualitative methods, such as case studies and expert survey data analyses. First, civil society development has stagnated since accession and so has its otherwise positive influence on corruption control: the exodus of most external donors and the EU's complicated procedures for applying for funding have crippled anti-corruption NGOs' capacities to monitor and advocate reforms. Second, EU leverage has been weaker after accession and anti-corruption reform has consequently slowed down: supranational pressures from the EU in the form of conditional funding and Cooperation and Verification Mechanism (in the cases of Bulgaria and Romania) as well as spillover effects from various chapters of the acquis have sufficed to prevent backsliding per se, but have not been able to reverse the post-accession trend of a slowdown in reform. Third, looking at corruption control as an independent variable, the effects of its stagnating trend post-accession include a decline in FDI. Encouraged by positive signaling from the EU confirming CEE countries' progression towards membership, FDI was steadily increasing during the pre-accession period and corruption control, improving or stagnant, was irrelevant for investors at that time. However, rates of investment have surprisingly dropped soon after accession, as investors have become less driven by cognitive shortcuts (the availability heuristic) causing them to assign disproportionate weight to information that is vivid or striking, such as the positive signals by the EU. In this new environment their concern about lack of progress in corruption control has led them to be more cautious.