Criminal law prohibits harmful acts through statutes and common law. It aims to protect the public from harm by punishing crimes that have occurred and preventing future harms. For an act to be considered a crime, it must violate a criminal law, be intentional, and have a prescribed punishment. Crimes vary in severity from mala in se offenses that are inherently wrong to mala prohibita offenses that are crimes due to restrictions placed on them. Criminal law is subject to constitutional limitations and requirements of due process and prohibitions on things like ex post facto laws and cruel and unusual punishment.