The Model Penal Code is a document designed as model for state criminal law in the United States. This statutory text, published by the The American Law Institute (ALI) in 1962, was an an attempt to encourage the standardization of criminal law across the states. The ALI, a non-governmental professional association for judges, lawyers and scholars, prepared its report after reviewing the penal laws in several states. It developed its recommendations after recognizing that criminal law in many states was not based on a central guiding philosophy; it was being developed spontaneously in response to various crimes as they were committed and caught public attention.
Most criminal law in the United States is a matter of state, not federal, law. The Model Penal Code was published with the hopes of influencing state legislatures to adopt a cohesive approach to the establishment of penal law. The code advocated the use of certain broad concepts, such as a criminal's state of mind, or mens rea, in determining the legal status of a crime and the severity of punishment. Under this principle, crimes committed with malicious intent are generally considered more serious than crimes that are the result of negligence or accident. The punishment for a crime, therefore, would differ depending on the perpetrator's thinking, even if the outcome was the same.
The Model Penal Code offers guidelines for arrest as well. For example, the code puts forward the principle that unless an act is actually forbidden in law, it should be considered legal. People should not be arrested and prosecuted for crimes that are not clearly defined, by law, as illegal.
The influence of the code on state criminal law has been mixed. State legislatures have adopted some aspects of the code and rejected others. For example, while the Modern Penal Code opposes the principle that a death that occurs in the course of a felony must be considered murder, this so-called felony murder rule remains the law in most of the United States.
It should also be noted that some of the Model Penal Code became outdated in its approach to certain crimes. The original code never mentioned drug offenses and did not criminalize marital rape. The ALI has also recognized that some of the code's prescriptions may be unworkable. For example, in 2009, the ALI voted to disavow its suggestions for the implementation of capital punishment, noting that it is impossible to reconcile the death penalty with oppressive social systems that inhibit fair sentencing.