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.

In theory, an indefinite prison sentence could be very short, or it could be a life sentence if no decision is made after sentencing to lift the term. In many cases, either a minimum term is imposed or the maximum that can be served is the maximum allowable by law in the jurisdiction for the particular offense.

Rationale.

The main reason for imposing indefinite (as opposed to fixed) sentences is to protect the community. An offender can then be kept behind bars until it is determined the offender would not pose any danger to society.

In some places, indefinite sentences have been around for a long time. In other jurisdictions, they have been introduced more recently.

United States.

Some US states have various forms of indefinite sentencing, and many have effective indeterminate sentencing with evaluation-based parole. The US federal prison system does not allow parole for any crimes committed after 1987. Therefore, a sentence of life imprisonment means that the prisoner will be incarcerated for life without parole.

Indeterminate sentencing existed in every U.S. state from the 1930s to the mid-1970s. The Model Penal Code, developed in the 1950s, focused on offenders' treatment needs rather than on retribution. Generous amounts of good conduct time could be awarded by prison officials. By the mid-1970s, indeterminate sentencing was under attack, as arguments were made that racial and other invidious biases influenced officials; that rehabilitative treatment programs were ineffective; and that broad, standardless discretion denied constitutional due process and permitted undue leniency that undermined the deterrent effects of sanctions.

Federal supervised release is also sometimes cited as an example of indeterminate sentencing.

Canada.

In Canada, an inmate classified as a dangerous offender can be given an indefinite prison sentence. That means the offender is at risk for causing a "serious personal injury."

United Kingdom.

England and Wales.

Imprisonment for public protection was a form of indefinite sentence that was used in England and Wales from 2005 until 2012, in addition to the traditional life sentence. The imprisonment for public protection sentence was abolished in 2012, but offenders already serving that sentence remained in prison.