While rooted in English common law, American substantive criminal law is statutory. There are no common law crimes in the United States. In other words, the law of crimes is decided by the state legislatures (for each state) and by Congress (for the federal government). Most states, but not the federal government, have a comprehensive "code" of substantive criminal law made up of general principles of criminal responsibility, laws defining the particular criminal offenses, and laws defining excuses and justifications.

Two-thirds of the states have adopted in whole or in part the Model Penal Code (MPC), which was drafted in the 1950s and 1960s by the American Law Institute, a prominent law reform organization. The MPC is the most influential work in American substantive criminal law.

One of the most deeply rooted principles in American criminal law is that there can be no criminal responsibility without culpability or blameworthiness. Under the MPC, culpability, sometimes referred to as mens rea or "state of mind," is satisfied by a showing of intent, knowledge, recklessness or negligence, all of which are carefully defined by the code. Except in the case of minor offenses and some regulatory crimes, the MPC requires that there be a specified culpability for every element of an offense (conduct, attendant circumstances, result).

Criminal codes set out the prohibitions that constitute the law of crimes -- offenses against a person (e.g. murder and rape); offenses against property (e.g. theft and arson); offenses against public order (e.g. disorderly conduct and rioting); offenses against the family (e.g. bigamy and incest); and offenses against public administration (e.g. bribery and perjury).