As of the mid-2020s, roughly eleven million people around the world were held in prisons and jails on any given day, according to the World Prison Brief, a database run by researchers in London. Prison is now the central punishment for serious crime in almost every country. What is it for, what is it like, and does it work?

Purposes

Prisons are asked to do several things at once: punish, deter, incapacitate dangerous people and rehabilitate. These aims can pull in different directions. A principle often attributed to the British prison commissioner Alexander Paterson in the early twentieth century states that people are sent to prison as punishment, not for punishment: the loss of liberty is itself the penalty, and prison conditions should not add further suffering.

Scale

Imprisonment rates vary enormously. As of the 2020s, many western European countries held fewer than 100 people per 100,000 residents; a few countries, including the United States, have had rates several times higher. Differences reflect crime levels, but also sentence lengths, drug policy, use of alternatives and how often people are held before trial. In many countries a large share of prisoners have not been convicted and are awaiting trial.

Conditions

Conditions range widely. Common problems include overcrowding, violence, poor health care, and high rates of mental illness and addiction. The United Nations Standard Minimum Rules for the Treatment of Prisoners, revised in 2015 and known as the Nelson Mandela Rules, set international standards. They prohibit prolonged solitary confinement, defined as more than 15 consecutive days, and require humane treatment, access to health care and contact with family.

Recidivism

Recidivism means reoffending after punishment. Many systems report that a substantial share of released prisoners return to crime within a few years. But the numbers are hard to compare, because countries measure different things over different periods: rearrest, reconviction or return to prison, after one, two or five years. Factors linked to lower reoffending include stable housing, employment, family ties, treatment for addiction and growing older.

Norway's model

Norway is often cited as a contrasting case. After reforms beginning in the 1990s, its prison service adopted a principle of normality: life inside should resemble life outside as closely as possible, apart from the loss of liberty. Most sentences are short. Officers receive extended training and are expected to talk with prisoners and help prepare them for release. Education, health and library services are provided by the same public agencies that serve everyone else. Halden Prison, opened in 2010, with private rooms and kitchens shared by small groups, became internationally famous.

Norway reports comparatively low rates of reconviction. Careful observers add caveats. Cross-country comparisons are difficult because definitions of recidivism differ, and Norway is a small, wealthy country with low inequality and a strong welfare system, so its results may not transfer easily. Its prisons are also expensive per prisoner, and Norwegian inspectors have themselves criticized aspects of the system, such as the use of isolation. Supporters reply that lower reoffending saves money and suffering over time.

Alternatives

Many countries rely heavily on non-custodial sentences: probation, community service, electronic monitoring, and fines. Finland and Germany use day fines, which are scaled to the offender's income, so that a fine weighs similarly on rich and poor. Debates continue about which offenders can safely be punished outside prison, and how to keep alternatives from simply adding more supervision to people who would otherwise have received none.

Worked example: two release days

Two invented men, Arto and Ben, are released on the same day after serving three years for similar burglaries in two different systems.

Arto served his sentence in an overcrowded prison. He shared a small cell with two others, spent most days locked in, and waited a year for a place in an education course that never opened. On release he receives a small sum of money and a bus ticket. He has no address, no job and a gap in his work history that employers notice. His old friends are the only people who call.

Ben served in a system built on the principle of normality. He lived in a small unit, cooked with other prisoners, worked in a workshop and finished a vocational certificate. In his final months he moved to a lower-security unit and was allowed to work outside during the day. Before release, his case worker arranged housing and contact with the local employment office.

Which man is more likely to reoffend? The factors linked to lower recidivism, such as housing, work, family ties and skills, all favor Ben. But note the cautions from this level. A careful researcher would want to know whether the two systems hold similar kinds of people, how reoffending is measured, and what each approach costs. Ben's system spends more per prisoner; supporters argue that it saves money later if fewer people return.

The example does not settle how every prison should be run. It shows why the conditions inside, and not only the length of a sentence, may matter for public safety after release.