A central tool of the European Union (EU) to promote the democratization of post-communist Europe is its accession conditionality: the conditions it attaches to the offer of membership. Yet the EU’s influence on democratization varies across countries, and over time between the periods before and after accession. A key factor limiting the EU’s impact are the domestic costs of complying with the EU’s conditionality: the more governments rely on illiberal and undemocratic means to maintain power, the less influence the EU has. Moreover, even if the domestic adjustment costs are not prohibitively high, for EU conditionality to bring about, or lock in democratic change, the positive and negative incentives relating to the benefits of EU membership have to be credible. The limited credibility of the EU’s incentives, both of the sanctions against backsliding in new members and of the reward of accession for current candidate countries in Southeastern Europe, is a key explanation for the setback in the EU’s democratizing role during this decade.