Over the past years, energy security has turned into a major theme of the international security debate. As an Alliance that provides protection for almost 900 million citizens, NATO has a legitimate role to play in energy security. Defining the exact nature of this role proved difficult at first, as there were concerns by some Allies about unduly “militarizing” an essentially economic issue. But energy security is becoming firmly embedded in NATO’s agenda. The Alliance’s new Strategic Concept broke new ground with respect to non-traditional security challenges, including energy security. The Lisbon Summit Declaration also reinforced the Strategic Concept’s message by tasking NATO to integrate energy security considerations into NATO’s policies. Today, the question of “if” has been replaced by the question of “how” – energy security is now a permanent fixture of NATO’s agenda.