Criminal procedure: Sentencing: Life imprisonment + Indefinite imprisonment (indeterminate imprisonment) + habitual offender laws (three-strikes laws)

Life imprisonment is any sentence of imprisonment for a crime under which convicted people are to remain in prison either for the rest of their natural lives or until pardoned, paroled or otherwise commuted to a fixed term. Crimes for which, in some countries, a person could receive this sentence include murder, attempted murder, conspiracy to commit murder, apostasy, terrorism, severe child abuse, rape, child rape, espionage, treason, high treason, drug dealing, drug trafficking, drug possession, human trafficking, severe cases of fraud, severe cases of financial crimes, aggravated criminal damage in English law, and aggravated cases of arson, kidnapping, burglary, or robbery which result in death or grievous bodily harm, piracy, aircraft hijacking, and in certain cases genocide, ethnic cleansing, crimes against humanity, certain war crimes or any three felonies in case of three-strikes law. Life imprisonment (as a maximum term) can also be imposed, in certain countries, for traffic offenses causing death. Life imprisonment is not used in all countries; Portugal was the first country to abolish life imprisonment, in 1884.

Indefinite imprisonment or indeterminate imprisonment is the imposition of a sentence by imprisonment with no definite period of time set during sentencing. It was imposed by certain nations in the past, before the drafting of the United Nations Convention against Torture (CAT). The length of an indefinite imprisonment was determined during imprisonment based on the inmate's conduct. The inmate could have been returned to society or be kept in prison for life. Such a sentence is unconstitutional today, particularly in the United States.

In the United States, habitual offender laws (commonly referred to as three-strikes laws) were first implemented on March 7, 1994, and are part of the United States Justice Department's Anti-Violence Strategy. These laws require both a severe violent felony and two other previous convictions to serve a mandatory life sentence in prison. The purpose of the laws is to drastically increase the punishment of those convicted of more than two serious crimes.

Twenty-eight states have some form of a "three-strikes" law. A person accused under such laws is referred to in a few states (notably Connecticut and Kansas) as a "persistent offender", while Missouri uses the unique term "prior and persistent offender". In most jurisdictions, only crimes at the felony level qualify as serious offenses; however, misdemeanor and wobbler offenses can qualify for application of the three-strikes law in California, whose harsh application has been the subject of controversy.

The three-strikes law significantly increases the prison sentences of persons convicted of a felony who have been previously convicted of two or more violent crimes or serious felonies and limits the ability of these offenders to receive a punishment other than a life sentence.

The expression "Three strikes and you are out" is derived from baseball, where a batter against whom three strikes are recorded strikes out.