Criminal law is that part of public law that issues criminal sanctions to anyone who commits active or passive conduct that the legal system recognizes as crimes. The crime is any act or fact that the legal system recognizes as such. Any crime is such only if foreseen and recognized by law. According to the principle of determinacy, the penalty must be understandable to the point of making all subjects understand what the lawful conduct is and what the illegal conduct is.
There must be a proportion between penalty and crime, the penalty cannot be disproportionate to the crime committed (principle of proportionality).
Criminal law is only the ordinary law issued by the parliament, any law of lower rank is valid only for mere technical specifications (for example, to draw up what are the drugs).
The criminal law is valid only for the future, it is not possible to punish a fact that happened before the law came into force, therefore the criminal law is not retroactive.
In Italian criminal law, any new crime and security measure must be introduced into the criminal code by modifying its staff (principle of code reserve).