This ground-breaking study by Professor Einarsen seeks to clarify the concept of universal crimes in international law. It provides a new framework for understanding important features of this complex field of law concerned with the most serious crimes. Central issues include the following: What are the relevant crimes that may give rise to direct criminal liability under international law? Are they currently limited to certain core international crimes? Why should certain crimes be included whereas other serious offences should not? Should specific legal bases be considered more compelling than others for selection of crimes? The book is the first in a series entitled 'Rethinking the Essentials of International Criminal Law and Transitional Justice' (which also saw 'A Theory of Punishable Participation in Universal Crimes' published in 2018). The book is addressed to all with an interest in international criminal law and related disciplines like human rights, humanitarian law, and transitional justice. It makes an important contribution to a more coherent and practical understanding of international criminal law. The 2023 Persian edition is translated by Dr. Fereydoon Jafari.