The popular perception of the role of NATO was famously defined by NATO's first Secretary General, Lord Ismay, as 'keeping the Russians out, the Americans in and the Germans down'. NATO's role is still essentially to keep its members safe from threats, to ensure the cohesion of the transatlantic relationship, and to transform relations between former foes. However, behind this alluringly simple description of NATO, lie complex 'self', 'we' and 'other' definitions and perceptions of roles and relevant functional tasks. This paper seeks to unravel some of the complex processes of constituting and re-constituting NATO's roles. By utilizing a combination of role theory and social identity theory the paper traces how NATO has been engaged in complex and simultaneous processes of having a role set defined for it, whilst also being deeply involved in constructing its own identity and the identity of its member states, prospective member states and partners.