This chapter examines three Central and Eastern European EU members (Bulgaria, Lithuania, and Slovakia) that agreed to shut down their nuclear reactors not fulfilling the EU safety requirements during the accession process. Since this request was part of the membership requirements, conditionality seems to be able to explain their willingness to do such difficult step impacting their energy policies and energy security. However, while Bulgaria phased-out its reactors in Kozloduy already during the pre-accession process—in line with conditionality expectations—Lithuania and Slovakia did so only after they became full EU members in 2004. The puzzle this chapter is trying to shed light on is why these two countries fulfilled these (demanding and unpopular) obligations if the EU conditionality was not in place anymore. The chapter analyses factors that could have contributed to the post-accession compliance of Lithuania and Slovakia and thus contributes to the general discussion about the activities of Central and Eastern European countries in the EU.