Although it is often assumed that the principle of common but differentiated responsibilities (CBDR) has been the key instrument in structuring normative and practical functioning of the international climate regime, I argue that this principle has never become collectively shared and coherently applied. I propose three interrelated sites of contestation that have prevented this principle from reaching a status of a collectively shared norm: first, developed countries have failed to internalize it; second, developing countries have failed to unite behind it; and third, CBDR’s key tenets have become so fiercely contested that they have prevented coherent political implementation. This dynamic has undermined the legitimacy of the climate regime and disillusioned many members of the developing bloc. Since the CBDR principles are key to a well-functioning climate regime, a radical action by the developed countries must be taken to advance CBDR into a collective shared normative status and political guidance.