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What is criminal law?

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Key facts: Criminal law is a government-enforced system of rules defining crimes and punishments, codified separately by each state and by Congress in Title 18 of the U.S. Code, with some states modeling their codes on the Model Penal Code.[1][2]

Criminal law is the body of law concerned with crimes and the punishment of individuals who commit them, distinguishing it from civil law, where private parties dispute their own rights.[1]A criminal prosecution involves the government deciding whether to punish a person for an act or omission that a statute prohibits.[1]Both the federal government and each state maintain their own criminal codes, so the content of criminal law varies depending on the jurisdiction.[1]

Definition

Criminal law is a system of laws concerned with crimes and the punishment of individuals who commit them, as distinguished from civil law.[1]Where a civil case involves two parties disputing their rights, a criminal prosecution involves the government deciding whether to punish an individual for an act or omission.[1]A crime is any act or omission that violates a law prohibiting that action or omission.[1]Civil law, by contrast, regulates non-criminal legal relationships between individuals and encompasses areas such as contracts, torts, family law, property, and trusts.[3]For a closer comparison of the two systems, see criminal law vs civil law.

Substantive and procedural criminal law

Substantive criminal law defines what conduct counts as a crime and what the government must prove. In general, every crime involves three elements: the act or conduct (actus reus), the individual's mental state at the time of the act (mens rea), and causation between the act and the effect.[1]The statute creating an offense also establishes its elements, and the government carries the burden of proving each element beyond a reasonable doubt.[1]When a statute does not specify a mental state, courts will infer the mens rea "which is necessary to separate wrongful from innocent conduct".[1]These building blocks are discussed further at elements of a crime and mens rea.

Procedural criminal law governs how a criminal case moves through the system. Congress has codified federal criminal procedure in the Federal Rules of Criminal Procedure, alongside the substantive offenses listed in Title 18 of the U.S. Code.[1]Procedural rules also address matters such as liability for accomplices, including principals and accessories, and constitutional limits such as the prohibition on ex post facto laws and on punishing a person merely for a status rather than conduct.[1]The stages of a case, from arrest through trial, are covered at the criminal process step by step.

Purposes of punishment

Because a criminal prosecution is brought by the government rather than a private party, the central question in a criminal case is whether and how the government should punish an individual for an act or omission.[1]To carry out sentencing, the federal government and state governments have each created sentencing guidelines; federal courts use the Federal Sentencing Guidelines, while state courts apply their own state-specific guidelines.[1]Offenses are also graded by seriousness, which affects the available punishment: federal law classifies offenses into felony and misdemeanor classes based on the maximum authorized term of imprisonment, ranging from life imprisonment or death for a Class A felony down to five days or less, or no imprisonment at all, for an infraction.[4]General information on how sentences are determined appears at criminal sentencing.

Sources of criminal law

Criminal law in the United States comes from multiple sources. Each state decides what conduct to designate as a crime and maintains its own criminal code, and some of these codes, such as the New York Penal Law, closely follow the Model Penal Code.[1]The Model Penal Code was assembled by the American Law Institute and first promulgated in 1962; after its release, many states substantially reformed their criminal codes, and many still base their codes on it today.[2]The Model Penal Code has four parts, covering general principles of liability, definitions of specific offenses, treatment and correction, and the organization of corrections agencies, though the general-principles and specific-offenses parts have had the most lasting influence.[2]It also standardized mens rea terms used to describe a defendant's mental state and uses an elements analysis to separate the components of a crime required for liability.[2]Other criminal codes, including federal law, instead resemble the historical common law, which recognized major felonies such as murder, robbery, and burglary, and lesser misdemeanors such as assault and battery.[1]

Federal and state criminal law

Criminal laws vary significantly between the states and the federal government.[1]Congress has codified federal criminal law and procedure largely in Title 18 of the U.S. Code, sections 1 through 2725, designating conduct such as arson, use of chemical weapons, counterfeiting, embezzlement, espionage, genocide, and kidnapping as federal crimes, usually with a prescribed maximum sentence.[1]Federal criminal procedure itself is set out in the Federal Rules of Criminal Procedure, and additional federal regulations appear in 28 C.F.R..[1]Congress's power to create federal crimes is limited, because that power is generally reserved to the states, and as a result state criminal codes, such as the New York Penal Law, tend to be far more extensive than the U.S. Code; New York, for example, prescribes nine levels of felonies, ranging from residential mortgage fraud in the fourth degree to terrorism.[1]Both systems classify offenses by seriousness into felonies and misdemeanors, typically by the maximum authorized prison term.[5][6][4]More on these categories appears at felony vs misdemeanor vs infraction and on specific offense types at crimes and offenses and federal crimes.

Common questions

What does criminal law cover?

Criminal law covers crimes and the punishment of individuals who commit them, as distinguished from civil law, which concerns disputes between private parties over their own rights.[1]A crime is defined as any act or omission that violates a law prohibiting it, and the government, rather than a private party, decides whether to prosecute and punish the conduct.[1]

What are the main purposes of punishment?

Criminal prosecutions exist so that the government can decide whether to punish an individual for an act or omission, rather than leaving the matter to private parties as in a civil dispute.[1]To carry this out, federal and state governments use sentencing guidelines, and offenses are classified by seriousness, which affects the available punishment, such as the felony and misdemeanor classifications tied to maximum authorized prison terms.[1][4]

What are the two main branches of criminal law?

Criminal law involves substantive rules, which define the elements of an offense such as the act, the required mental state, and causation, and procedural rules, which govern how a case proceeds, including rules codified in the Federal Rules of Criminal Procedure.[1]Civil law, which governs private disputes over contracts, torts, property, and similar matters, is a separate system from criminal law.[3]

What is the Model Penal Code?

The Model Penal Code, or MPC, is a model code assembled by the American Law Institute and first promulgated in 1962.[2]Following its release, many states significantly reformed their criminal codes, and many state codes are still based on the MPC today, which standardized mens rea terms and used an elements analysis to define liability.[2]

How does a felony differ from a misdemeanor?

A felony and a misdemeanor are both types of offenses punishable under criminal law, but they are distinguished chiefly by the length of the maximum authorized term of imprisonment.[5][6]Under federal law, a felony generally involves a maximum sentence of more than one year, while a misdemeanor involves a maximum sentence of one year or less, down to an infraction if five days or less, or no imprisonment is authorized.[4]

References

All sources retrieved November 2026.

  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z 26 27 28 29 "Criminal law (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
  2. ^ a b c d e f g "Model Penal Code (MPC) (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
  3. ^ a b c "Civil law (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
  4. ^ a b c d "18 U.S.C. § 3559". U.S. Code via Legal Information Institute. Retrieved November 2026.
  5. ^ a b "Felony (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
  6. ^ a b "Misdemeanor (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.