The penal legislation of the Republic of Kazakhstan includes a number of crimes against the peace and security of mankind. Among these are most of the traditional “core” crimes under international law—genocide, war crimes, and the crime of aggression—as well as some other crimes. Crimes against humanity are not included in the Criminal Code so far but some of their definitional features are shared by so-called “extremist crimes”. In addition to other customary crimes against the peace and security of mankind—such as deliberately attacking internationally protected persons and organizations and abusing internationally protected emblems—the Code also includes more novel crimes, such as participation in foreign armed conflicts. This paper analyses the relevant provisions of the Criminal Code of Kazakhstan in the light of corresponding treaty-based and customary rules of international law, and suggests further improvements to be made to the Code.