Energy policy is concerned with the production, utilization, transport, and supply of primary energy and secondary energy. This chapter identifies and explains the policy constraints that have inhibited progress in European Union (EU) energy integration. It provides a historical overview of the evolution and development of EU energy policy. The chapter explores contributions dealing with EU energy policy from a public policy perspective. EU energy is characterized by both issue complexity and institutional complexity. Energy has a strategic dimension because the availability of energy is a prerequisite for the functioning of an industrialized or developing country. The temporal dimension involves path dependencies resulting from long construction times and life of energy infrastructures. The awareness of climate change led to the promotion of renewable sources of energy and energy efficiency and to the creation of an emissions trading system. Energy policy has become a "hot topic in the EU's political agenda".