This volume of the Netherlands Yearbook of International Law (NYIL) addresses the question how the assumption that states have a common obligation to achieve a collective public good can be reconciled with the fact that the 195 states of today’s world are highly diverse and increasingly unequal in terms of size, population, politics, economy, culture, climate and historical development.  The idea of common but differentiated responsibilities is on paper the perfect bridge between the factual inequality and formal equality of states. The acknowledgement that states can have common but still different – more or less onerous – obligations is predicated on the moral and legal concept of global solidarity.  This book encompasses general contributions on the function and the content of the related principles, chapters that describe and evaluate how the principles work in a specific area of international law and chapters that address their efficiency andbroader ramifications, in terms of compliance, free-rider behaviour and shifting balances of power.  The originality of the book resides in the integration of conceptual, comparative and practical dimensions of the principles of global solidarity and common but differentiated responsibilities. The book is therefore highly recommended reading for both academics with a theoretical interest and those working within international organisations. The Netherlands Yearbook of International Law was first published in 1970. It offers a forum for the publication of scholarly articles in a varying thematic area of public international law.