This is the first volume to appear in the book series Shared Responsibility in International Law. It was produced as part of the research project on Shared Responsibility in International Law (SHARES), which has been carried out at the Amsterdam Center for International Law (ACIL) of the University of Amsterdam from 2010 onwards. This book series provides new perspectives on responsibility problems that arise from the increasing number of situations in which states, international institutions, and other actors engage in concerted action in the pursuit of common objectives. While such concerted action generally aims to provide beneficial outcomes, all too often it has resulted in harmful ones. If that is the case, the multiplicity of actors involved in the concerted actionmay complicate the determination and implementation of international responsibility. The book series examines the grounds on which international law does and should allow for shared responsibility between all actors involved, and how it can be developed in a way that better enables the determination and implementation of shared responsibility. This first volume lays the groundwork for the series as a whole by critically reviewing the established principles of international responsibility as developed by the International Law Commission (ILC) – that are widely considered to be the state of the art in the law of international responsibility – from the perspective of shared responsibility. It discusses whether these principles allow for and support the determination and/or implementation of shared responsibility, whether they provide useful guidance for the often complex questions of distribution of international responsibility, or whether they contain obstacles. The volume also identifies any developments that might de lege ferenda provide for a better fit between the law of responsibility and shared responsibility.