Looking back at NATO’s Libya campaign, Secretary General Anders Fogh Rasmussen made the Alliance appear as an effective crisis manager that made the difference between life and death for many Libyans (Rasmussen, A F 2011, “Towards NATO’s Chicago Summit”). Yet, the idea of NATO as a “force for good” that acitvely shoulders responsibilities for civilians in non-member states is contested. Diverging views on NATO’s responsibilities and area of responsibility is one key aspect of the difficulties to uphold a commonality of ‘transatlantic’ interests and norms. The Libya campaign was preceded by the Strategic Concept debate, during which the Alliance’s tasks were intensely debated. At the Lisbon summit of 2010 NATO decided to take on an ambitious agenda, in theory shouldering responsibility for everything from defense of territory to regional and global security. Yet, what does this agenda signify and how is it circumscribed by diverging interpretations of NATO’s responsibilities? This paper suggests a research agenda that focuses on tensions within NATO that emerge from diverging notions of responsibility. While the emerging norm of a “Responsibility to Protect” denotes a particular and narrow outlook on responsibility, this paper proposes a broader and deeper understanding of the notion of responsibility. It begins with a theoretical exploration of the significance and meaning of responsibility in the global security environment, after which it takes on the question of diverging notions of responsibility within NATO and possible consequences for the future of the Alliance in terms of practical tasks and Alliance cohesion.