We use the two main theoretical perspectives analyzing traditional accounting disclosure : the firm as a nexus of contracts and agency theory on the one hand, and neo-institutional and legitimacy theory on the other, in order to assess the environmental and social reporting practices and the main international standardization process : Global Reporting Initiative (GRI). Through the accounting perspective, we analyze the standard-setting process and its actors, the stakes and limits of the conceptual framework and the report content ; we highlight the ambiguity of the role played by these reportings and their targeted users. From a technical point of view, this analysis provides evidence that GRI guidelines have to be strongly improved to become close to “generally accepted" accounting standard . From a political point of view, GRI appears as a private standardization institution promoting a framework for voluntary sustainability reporting faced with the risk of stronger disclosure requirements.