The term criminal law can be confusing. This is because some sources use it in a very general way to describe the entire spectrum of laws dealing with the criminal justice system; others use it as a shorthand way of referring to what is also known as the substantive criminal law. This text follows the latter approach by using the heading criminal law to refer to the substantive criminal law, which is the part of the law that describes what acts are prohibited and what punishments are associated with those acts. Also included are legal defenses (such as the insanity defense) that apply in criminal cases.

A common way of organizing criminal laws is to divide them into felonies and misdemeanors, which depend largely on the seriousness of the offense and the type of punishment associated with the offense. Things like petty thefts, simple assault, disorderly conduct, and public drunkenness are relatively nonserious crimes classified as misdemeanors. Misdemeanors are usually only punishable by fine and imprisonment in a local jail for a period of less than a year. Felonies, on the other hand, are serious crimes (e.g., rape, murder, burglary, kidnapping) where the punishment can be death or a long period (at least a year) of incarceration in a state-run prison. Note that this distinction depends on the sentence; some convicts go to prison for less than a year because of early release programs such as “good time” and parole.

There is also a distinction between types of criminal law based in the inherent evil of the act. If the act is “wrong in itself,” it is considered a mala in se offense. If an act is not necessarily evil and is only considered criminal because it is prohibited by the government, it is considered a mala prohibita offense. Most so-called “victimless crimes” are mala prohibita offenses. Because people’s views vary so widely as to the inherent wrongness of an act, there is no absolute standard for classification.

Criminal acts that are highly visible to the public are often referred to as visible crime, ordinary crime, or street crime. The overt nature of such crimes makes notice by police more likely, and thus prosecution more likely. Murder is a common example: Most murders come to the attention of the police, and prosecution is more likely than for most other offenses. Occupational crimes are less obvious. These are crimes that a particular job provides the criminal opportunity. The most common example is embezzlement. Crimes committed by groups with a discernable organizational structure are classified as organized crime. Organized crime is considered especially heinous because groups can cause more criminal damage, and the groups make for more difficult investigations and prosecutions.

A large swath of criminal offenses involving computers and related technologies are collectively known as cybercrime. Cybercrime involves disparate acts such as distributing child pornography, sending out mass emails in an attempt to obtain identifying information (phishing), distributing viruses designed to damage computer systems, hacking into business computers to steal money, and so forth.

Crimes that are motivated by bias toward a particular race, religion, ethnicity, or sexuality are known as hate crimes.

Criminal versus Civil Law

In civil law, a wrong done to another person is called a tort. When a harmed individual (the plaintiff) wins a tort case in civil court, they may also win a money award referred to as damages. In other words, torts are private wrongs. A criminal prosecution operates under a different legal theory. A crime, the theory holds, may harm the individual, but it also harms all of society. Since the people are represented by the state, all criminal prosecutions are brought forward in the name of the state. What the “state” calls itself can vary from state to state; some prosecutions are done in the name of the people, and some are done in the name of the “commonwealth.” Regardless of how the case is named, a prosecutor working for the government on behalf of society brings it forward.

It is important to note that the criminal system and the civil system sometimes interact. A person can be found guilty of a crime in criminal court and found liable for a tort for the exact same behavior. In addition, individuals that have suffered losses due to criminal actions can sometimes use the civil courts to recoup their losses.

State versus Federal Crimes

While the United States is a common law country, most criminal laws are a matter of statutes today. An essential difference between a state criminal statute and a federal criminal statute is that federal laws will usually contain a jurisdictional element. Because of the constitutional limits placed on the authority of Congress to make criminal laws, federal criminal statutes must be tailored to a particular power delegated to Congress, such as the power to regulate interstate commerce. Most criminal laws exist on the state level because of this limitation.

When a particular act is criminal on both the state and federal levels, there is overlapping jurisdiction in the case. As a matter of constitutional law, the person could be prosecuted on both the state and federal levels. In practice, this rarely happens. In a few high-profile cases, federal prosecutors have taken up a case when the public widely perceived that justice was not done in state courts (e.g., the Rodney King police brutality case).