The G‐20 is one of the biggest institutional innovations in the area of international economic governance. Following this evolution, some scholars have already talked about a ‘global leadership in transition,’ while others are more reluctant to the very idea of having –even with twenty members– a restricted forum. Through this paper I have addressed the circumstances around the rise of the G‐20, how these events shaped the way in which this forum would operate, its problems of legitimacy, and above all whether it is a viable proposition capable of being the “apex governing body of the Bretton Woods organizations”. To better explore the type of institutional architecture suitable to this group, I have drawn on the works of Robert Wade, Dani Rodrik and other relevant literature relating to the subject. Special attention has been given to the problem of input and output legitimacy to show that the major legitimacy problem –contrary to the opinion of several authors– is not at the representation level (input legitimacy) but at the level of G‐20’s effectiveness and results (output legitimacy).