In this article, through the comparative legal analysis of domestic, as well as foreign constitutional and criminal law norm content, various approaches to the principle of legality and its main features were examined. The authors have studied various ways of this principle criminal legal regulation and the problems that arise in this regard. It was concluded that the principle of legality has a different degree of certainty in the criminal legislation of different countries. This creates the conditions conducive to the making of unlawful judicial decisions that undermine the authority of national courts and compel people to apply for protection to supranational courts.