This study analyses the expansion of the EU into energy market regulation. It shows that the limits to EU influence and, thereby, EU energy market regulation for the internal energy market, begin where EU influence affects national interests with regard to ensuring energy security. This scientifically established insight bears an important practical implication. The further development of EU energy market regulation as a cornerstone of the internal energy market faces a particular policy challenge: It is necessary to establish a regulatory framework for the internal electricity and gas market, which acknowledges the primacy of national energy security interests. This finding is important in the light of the new and increasing energy policy challenges that some Member States face today, not least as a result of a liberalized energy market. Moreover, in the context of new systemic risks arising from ongoing energy market integration, a politically unstable (in the worst case - collapsing) EU regulatory framework can cause significant social and economic costs for individual Member States. With regard to that, the study points to the increasingly complex policy areas that are made subject to EU integration and calls for more attention to the related regulatory and political risks - also with a view to the current euro crisis.