The present book is based on the lectures delivered by the author in the past few years as part of the Criminal Law course of the Faculty of Law at the Ono Academic College. There has been little research on the principle of legality in modern criminal law, although this is one of the most ancient legal principles of human society. In recent generations there have been several attempts to define the principle conclusively, but only with regard to some of its aspects. No comprehensive definition of the principle of legality has been attempted to date