This chapter introduces the concept of cultural cosmopolitanism as the third thinking tool with a view to framing the theory of contestation. This thinking tool is developed with recourse to Tully’s “public philosophy in a new key” (Tully 2008a, b). From this background, the application of this thinking tool towards a critical investigation into international relations theories is aimed to identify the interrelation between the practice of contestation and the principle of contestedness. This is done with reference to the feature of three degrees of contestation (i.e. low, high and regular) in relation with the three types of norms. Understood as a norm-generative practice contestation is considered as a sine qua non for legitimacy in any context of governance. It is argued that, in order to make full use of the concept, ‘regular’ contestation ought to be established as a legitimacy enhancing practice in the global realm. This chapter works with ‘cultural cosmopolitanism’ as a thinking tool to demonstrate the normative effect of cultural practices in inter-national relations as individual experiences, rather than collective, cultural properties.