Although two of the three original treaties of European Union (EU) were related to energy resources (coal and nuclear resources), yet a detailed legal basis for EU energy policy was absent in the most important EC Treaty (TEC) for a longtime. Currently, this situation is eventually altered by the Treaty of Lisbon which formally established a new legal basis of energy policy. However, relatively little research attention so far seems to have been devoted to a comprehensive study about this new legal basis and its relation with other parts of the Treaty. Therefore, this thesis aims to explore the energy-related content of Lisbon Treaty. It proposes at three levels as follows. First, the new legal basis clause and the competence delimitation of energy policy are most conspicuous breakthroughs presented by the Treaty. At the first time, EU energy policy has a detailed legal basis as well as a transparent competence division between the Union and Member States. They provide a comprehensive set of rules about the objectives, legal framework, decision-making procedure and competence allocation in this area. Therefore, these two provisions are breakthroughs brought by the Treaty. Second, apart from the new legal basis, numerous legal bases of other areas stress energy-related matters as well, such as the legal basis of environmental policy. This phenomenon clearly illustrates there are certain interfaces between energy policy and other relevant policy areas. In fact, entire objectives which stipulated in the new legal basis of energy policy have certain interfaces with other four provisions in the TFEU. Therefore, this thesis also examines these interfaces. Third, in the practical level and in order to safeguard the security of energy supply, EU needs to strengthen its relations with energy partners. In this regard, the Treaty of Lisbon also introduces institutional innovations in the Common Foreign and Security Policy. These innovations could be viewed as an opportunity for the EU to tackle the energy challenge of Europe in a better way. The thesis evaluates possible impacts of new actors in the external energy field and provides a preliminary observation on daily practices of them in the post-Lisbon period. As a conclusion, the major finding of thesis argues that the contribution of Treaty to energy policy is between fundamental breakthrough and challenge ahead. Therefore, it iv still depend upon the actors of this policy area to better make use of breakthroughs, organize the interfaces and seize the opportunity provided by the Treaty and further develop this vital policy area in the future.