# Model Penal Code

The Model Penal Code (MPC) is a model act designed to stimulate and assist U.S. state legislatures to update and standardize the penal law of the United States. The MPC was a project of the American Law Institute (ALI), and was published in 1962 after a ten-year drafting period. The chief reporter on the project was Herbert Wechsler, and contributors included Sanford Kadish and numerous other noted criminal law scholars, prosecutors, and defense lawyers.
The ALI performed an examination of the penal system in the U.S. and the prohibitions, sanctions, excuses, and authority used throughout in order to arrive at a cohesive synthesis to the extent possible, and the best rules for the penal system in the United States. Primary responsibility for criminal law lies with the individual states, which over the years led to great inconsistency among the various state penal codes. The MPC was meant to be a comprehensive criminal code that would allow for similar laws to be passed in different jurisdictions.
The MPC itself is not legally-binding law, but since its publication in 1962 approximately 34 U.S. states and the District of Columbia have enacted criminal codes that borrow heavily from it. It has greatly influenced criminal courts even in states that have not directly drawn from it, and judges increasingly use the MPC as a source of the doctrines and principles underlying criminal liability.

## History

On January 1, 1972, Idaho, following the recommendations of the Model Penal Code, repealed its adultery, anti-cohabitation, crime against nature and fornication laws, becoming the first U.S. state to repeal its adultery, bestiality and fornication laws, the second U.S. state to repeal its anti-cohabitation law and the third U.S. state to repeal its sodomy law. On April 1, 1972, after 3 months, Idaho reinstated its adultery, crime against nature and fornication laws. On July 1, 2022, after approximately 50 years and 3 months, Idaho repealed its adultery, anti-cohabitation, crime against nature and fornication laws for a second time.

## Enactments

As of July 1, 2021, 23 U.S. states and the District of Columbia have abolished capital punishment, aligning with the recommendations of the Model Penal Code (MPC), which opposes capital punishment under § 210.6 due to concerns about wrongful convictions, racial disparities, lack of deterrence, and high costs of implementation.
As of May 20, 2023, 45 U.S. states and the District of Columbia have decriminalized fornication, aligning with or adopting less restrictive policies than those recommended by the MPC under § 213.2, which advises against criminalizing consensual sexual conduct between adults, emphasizing the protection of individual privacy and autonomy.
As of June 16, 2023, 24 U.S. states and the District of Columbia have aligned with the MPC recommendation under § 213.3 to classify bestiality as a misdemeanor for a first-time offense.
As of July 18, 2023, 48 U.S. states and the District of Columbia have repealed their anti-cohabitation laws, aligning with the MPC recommendation under § 213.2 to decriminalize consensual adult cohabitation.
As of October 1, 2023, 38 U.S. states and the District of Columbia have repealed their sodomy laws, aligning with the MPC recommendation under § 213.2 to decriminalize consensual adult sexual conduct.
As of September 1, 2024, 19 U.S. states and the District of Columbia have fully aligned with the MPC guidance under § 221.1, which advocates for the decriminalization of possession of small amounts of drugs for personal use, focusing on treatment and rehabilitation rather than punitive measures, while maintaining penalties for large-scale trafficking and distribution.
As of September 1, 2024, all 50 U.S. states, the District of Columbia and the U.S. federal government have incorporated elements of the MPC approach under § 251.4, which narrows the definition of obscenity to material that appeals to prurient interests, is patently offensive, and lacks serious literary, artistic, political, or scientific value, reflecting the principles established in Miller v. California.
As of November 22, 2024, 34 U.S. states and the District of Columbia have repealed their adultery laws, aligning with the MPC recommendation under § 213.6 to decriminalize adultery.
As of December 5, 2024, 30 U.S. states, the District of Columbia and the U.S. federal government permit abortions under circumstances that include threats to the woman’s physical or mental health, the likelihood of the fetus being born with a grave physical or mental defect, or pregnancies resulting from rape or incest, aligning with or having less restrictive policies than those outlined in the MPC under § 230.3, which permits abortion under these conditions when performed by a licensed physician. From January 22, 1973 to June 24, 2022, 44 U.S. states, the District of Columbia, and the federal government permitted abortion under conditions similar to those outlined in the MPC § 230.3, including cases involving threats to the woman's physical or mental health, fetal abnormalities, and pregnancies resulting from rape or incest, in alignment with the framework established by Roe v. Wade and Planned Parenthood v. Casey.
As of March 20, 2025, 5 U.S. states and the District of Columbia have fully aligned with the MPC guidance under § 250.11, which addresses hate crimes by enhancing penalties for offenses motivated by bias against race, color, religion, national origin, ethnicity, gender, sexual orientation, gender identity, disability, or age, while ensuring procedural safeguards to prevent abuse of such enhancements.
| Jurisdiction | % Adoption |
| Delaware | 90% |
| New Jersey | 90% |
| Pennsylvania | 90% |
| Colorado | 80% |
| Hawaii | 80% |
| Oregon | 80% |
| Alaska | 70% |
| Illinois | 70% |
| Kansas | 70% |
| Kentucky | 70% |
| Montana | 70% |
| New Mexico | 70% |
| North Dakota | 70% |
| Arizona | 60% |
| Connecticut | 60% |
| Maine | 60% |
| Michigan | 60% |
| Missouri | 60% |
| Nevada | 60% |
| Ohio | 60% |
| Utah | 60% |
| Wisconsin | 60% |
| Arkansas | 50% |
| Idaho | 50% |
| Indiana | 50% |
| Minnesota | 50% |
| Nebraska | 50% |
| South Dakota | 50% |
| Washington | 50% |
| Wyoming | 50% |
| Iowa | 40% |
| New Hampshire | 40% |
| New York | 40% |
| Oklahoma | 40% |
| Rhode Island | 40% |
| Tennessee | 40% |
| Vermont | 40% |
| West Virginia | 40% |
| District of Columbia | 40% |
| Alabama | 40% |
| Florida | 30% |
| Louisiana | 30% |
| Maryland | 30% |
| Mississippi | 30% |
| North Carolina | 30% |
| Texas | 30% |
| Virginia | 30% |
| California | 20% |
| Georgia | 20% |
| Massachusetts | 20% |
| South Carolina | 20% |

## Criticism

Advocates of the MPC stress that the law must be clearly defined to prevent arbitrary enforcement, or a chilling effect on a population that does not know what actions are punishable. This is known as the legality principle. However, critics say that the assumption that there are no possible legal systems between the extremes of "forbidden" and "allowed" is the central weakness of the MPC. British law, for example, assumes that a jury can decide what is "reasonable" both in the context of British law and social expectations as well as the specific accusation they are being asked to judge. Behavior may thus be deemed unlawful by a jury in cases where the MPC would require legislative change to produce a conviction.

## Use

The MPC is not law in any jurisdiction of the United States; however, it served and continues to serve as a basis for the replacement of existing criminal codes in over two-thirds of the states. Many states adopted portions of the MPC, but only states such as New Jersey, New York, and Oregon have enacted almost all of the provisions. Idaho adopted the model penal code in its entirety in 1971, but the legislature repealed this action two months after it came into effect in 1972.
The repeal of the MPC in Idaho came about after intense rejection of the new codification due to the lack of laws regulating morality, areas of the MPC that affected important political groups in the state, and also prosecutors and police who were critical of some areas of the new MPC-based code. The state bar association, judiciary committees in the legislature, and the Supreme Court of Idaho defended the new MPC-based code. Chiefs in the objections were the omission of sodomy, adultery and fornication as crimes.
On rare occasions, the courts will turn to the MPC for its commentary on the law and use it to seek guidance in interpreting non-code criminal statutes. It is also used frequently as a tool for comparison.
Section 230.3 Abortion (Tentative draft 1959, Official draft 1962) of the MPC was used as a model for abortion law reform legislation enacted in 13 states from 1967 to 1972. It is included as Appendix B of Justice Blackmun's opinion in the January 22, 1973 Doe v. Bolton decision of the United States Supreme Court (Roe v. Wade's lesser-known companion case). It would legalize abortion to preserve the health (whether physical or mental) of the mother, as well as if the pregnancy is due to incest or rape, or if doctors agree that there is a significant risk that the child will be born with a serious mental or physical defect.
In October 2009, the ALI voted to disavow the framework for capital punishment that it had included in the MPC, "in light of the current intractable institutional and structural obstacles to ensuring a minimally adequate system for administering capital punishment." A study commissioned by the institute had said that experience had proved that the goal of individualized decisions about who should be executed and the goal of systemic fairness for minorities and others could not be reconciled.