The notion of responsibility in international law involves the violation of an international obligation for which a State can be held liable. The concept of common but differentiated responsibilities (CBDR) however does not squarely fit within the traditional scenario of state responsibility. Primarily based on the notions of equity and justice and premised in particular upon the principle of intra-generational equity, CBDR, as a structuring principle of the international legal order, hinges upon responsibility in its moral dimension. Its application involves the elaboration of differentiated legal standards and commitments according to both responsibilities and capabilities of States. This chapter argues that because it is premised on the notions of equity and justice, the principle of CBDR necessarily calls for a broadening of the understanding of responsibility in international law, yet, it is suggested that, beyond the moral dimension of responsibility that is referred to, CBDR may still impinge upon the assessment of international responsibility in its purely legal dimension and constitute a standard against which a State’s liability will be evaluated.