The aim of this paper is to identify the main challenges regarding the achievement of a low-carbon energy system in the EU by 2050. The authors analyze the visions presented by stakeholders and existing strategies of member state to achieve this transition. The five main challenges identified are the following: 1. energy efficiency - to ensure ambitious energy savings; 2. GHG emissions- to go towards a nearly zero-carbon electricity system; 3. renewable energy - to push effective technologies into the market; 4. energy infrastructure - to ensure timely investment in the electricity transmission grid capacity across borders; 5. energy markets - to guarantee timely investment in electricity generation back-up capacity.