This chapter clarifies some key terms and situates the phenomenon of sharing international obligations within the current body of international legal doctrine. The conceptualization of shared obligations takes place in the context of the international law of obligations, and it is first discussed what is meant when reference is made to this body of law. The focus then turns to the concept of shared responsibility in international law, and some preliminary reflections are offered on how the concept of shared obligations contributes to the ongoing discussion on problems of shared responsibility in legal doctrine. It is then discussed how the idea of sharing international obligations has been recognized in international legal literature and proceedings before international courts, reflecting an (at times implicit) assumption that the sharing of international obligations has relevant legal implications. Nevertheless, the notion of shared obligations remains conceptually underdeveloped. Finally, it is set out how this lack of conceptualization of shared obligations is not a result of the notion’s irrelevance but may be explained – at least in part – by a few fundamental choices that have been made during the ILC’s project of codification and progressive development of the international law of obligations.