In this book, Elies van Sliedregt examines the concept of individual criminal responsibility for violations of international humanitarian law, including genocide, crimes against humanity and war crimes. Such crimes are very rarely committed by single individuals, but mostly by organizations or groups of cooperating persons. For a just determination of their guilt and responsibility, a fair assessment of the mutual relationships and cooperation forms of those individuals is indispensable. This book provides the framework for that assessment. It gives guidance to practitioners and scholars on how to understand and to apply international criminal law concepts such as 'common purpose', 'superior responsibility', 'duress' and the 'defence of superior orders'. It does so by bringing to light the roots of those concepts, which are hidden not only in earlier phases of development of international criminal law, but also in the domestic laws of various states.