The Energy Union is the European Commission’s flagship initiative for Europe’s energy future. Building on existing EU energy policies, the European Commission laid out its Energy Union Strategy in February 2015 to achieve the objectives of moving away from an economy driven by fossil fuels, providing a new deal for consumers and overcoming the current fragmentation of a European energy system currently characterised by uncoordinated national policies. This chapter attempts to shed light on the Energy Union. It firsts puts the Energy Union in context, and then studies it under each of its dimensions: energy security, an integrated European energy market; energy efficiency; decarbonisation; and research, innovation and competitiveness. It concludes by saying that the Energy Union project is much more than a slogan, at least in the eyes of the European Commission. It then proposes fields for further research that may shed further light on the Energy Union in particular, and EU energy policy in general.