The accession of Bulgaria and Romania to the European Union in 2007 offers significant theoretical and empirical insights into the way in which the EU has deployed and realised its enlargement strategy/strategies over the past 15 years. Borrowing from the literature on enlargement-led Europeanisation and EU conditionality, this article discusses how the EU has sought to influence domestic reform in the two countries through a mix of threats and rewards. What emerges from Bulgaria and Romania’s trajectory towards EU membership is the evolutionary and contested nature of EU conditionality as well as the considerable EU discretion in the manner of its implementation. In that sense Bulgaria and Romania, as ‘outliers’ of the 2004–2007 EU enlargement, offer us critical tests of the enlargement-led Europeanisation thesis. Thus, this study provides useful conceptual insights into the transformative power of the EU in Central and Eastern Europe and highlights important policy legacies affecting the current EU enlargement strategy in the Western Balkans and Turkey.

Whilst often regarded as the ‘procedural’conclusion of the 2004 enlargement round, the accession of Bulgaria and Romania into the European Union in 2007 offers significant theoretical and empirical insights into the way in which the EU has deployed and realised its enlargement strategy/strategies over the past 15 years. Ever since their turbulent transition to democracy in the early 1990s, the two countries have experienced difficult relations with the EU. For officials in Brussels the slow pace of democratic consolidation and domestic economic reform has been a regular