There are various situations in which multiple states or international organizations are bound to an international obligation in the context of cooperative activities and the pursuit of common goals.This practical phenomenon of sharing international obligations raises questions regarding the performance of obligations (who is bound to do what) and international responsibility in case of a breach (who can be held responsible for what).This book puts forward a concept of shared obligations that captures this practical phenomenon and enables scholars and practitioners to tackle these questions.In doing so, it engages in positive law-based categorization and systematization, building on existing categorizations of obligations and putting forward new typologies of shared obligations.Ultimately, it is contended that the sharing of obligations has relevant legal implications: it can influence the content and performance of obligations as well as the responsibility relations that arise in case of a breach.