Energy policy has been considered as a “special case of Europeanization,” due to its tardy and patchy development as a domain of EU activity as well as its important but highly contested external dimension. Divergent energy pathways across Member States and the sensitivity of this policy domain have militated against a unified European Energy Policy. And yet, since the mid-2000s cooperation in this policy area has picked up speed, leading to the adoption of the Energy Union, presented by the European Commission as the most ambitious energy initiative since the European Coal and Steel Community. This dynamism has attracted growing scholarly attention, seeking to determine whether, why and how European Energy Policy has consolidated against all odds during a particularly critical moment for European integration. The underlying question that emerges in this context is whether the Energy Union represents a step forward towards a more homogenous and joined-up energy policy or, rather a strategy to manage heterogeneity through greater flexibility and differentiated integration. Given the multilevel and multisectoral characteristics of energy policy, answering these questions requires a three-fold analysis of (1) the degree of centralization of European Energy Policy (vertical integration), (2) the coherence between energy sub-sectors (cross-sectoral integration), and (3) the territorial extension of the energy acquis beyond the EU Member States (horizontal integration). Taken together, the Energy Union has catalyzed integration on the three dimensions. First, EU institutions are formally involved in almost every aspect of energy policy, including sensitive areas such as ensuring energy supplies. Second, the Energy Union, with its new governance regulation, brings under one policy framework energy sub-sectors that had developed in silos. And finally, energy policy is the only sector that has generated a multilateral process dedicated to the integration of non-members into the EU energy market. However, this integrationist dynamic has also been accompanied by an increase in internal and external differentiation. Although structural forms of differentiation based on sectoral opt-outs and enhanced cooperation have been averted, European Energy Policy is an example of so-called “micro-differentiation,” characterized by flexible implementation, soft governance and tailor-made exemptions and derogations.