Penal labour or prison labour is a term for various kinds of forced labour that prisoners are required to perform, typically manual labour. The work may be light or hard, depending on the context. Forms of sentence involving penal labour have included involuntary servitude, penal servitude, and imprisonment with hard labour. The term may refer to several related scenarios: labour as a form of punishment, the prison system used as a means to secure labour, and labour as providing occupation for convicts. These scenarios are sometimes applied to those imprisoned for political, religious, war, or other reasons as well as to criminal convicts.

Large-scale implementations of penal labour include labour camps, prison farms, penal colonies, penal military units, penal transportation, or aboard prison ships.

Punitive labour, also known as convict labour, prison labour, or hard labour, is a form of forced labour used in both the past and the present as an additional form of punishment beyond imprisonment alone. Punitive labour encompasses two types: productive labour, such as industrial work; and intrinsically pointless tasks used as primitive occupational therapy, punishment, or physical torment.

Sometimes authorities turn prison labour into an industry, as on a prison farm or in a prison workshop. In such cases, the pursuit of income from their productive labour may even overtake the preoccupation with punishment or reeducation as such of the prisoners, who are then at risk of being exploited as slave-like cheap labour (profit may be minor after expenses, e.g. on security). This is sometimes not the case, and the income goes to defray the costs of the prison.

Victorian inmates commonly worked the treadmill. In some cases, it was productive labour to grind grain (an example of using convict labour to meet costs); in others, it served no purpose. Similar punishments included turning the crank machine or carrying cannonballs. Semi-punitive labour also included oakum-picking: teasing apart old tarry rope to make caulking material for sailing vessels.

In a number of penal systems, inmates have the possibility of getting jobs. This may serve several purposes. One goal is to give an inmate a meaningful way to occupy their prison time and a possibility of earning some money. It may also play an important role in resocialisation as inmates may acquire skills that would help them to find a job after release. It may also have an important penological function: reducing the monotony of prison life for the inmate, keeping inmates busy on productive activities, rather than, for example, potentially violent or antisocial activities, and helping to increase inmate fitness, and thus decrease health problems, rather than letting inmates succumb to a sedentary lifestyle.

The classic occupation in 20th-century British prisons was sewing mailbags. This has diversified into areas such as engineering, furniture making, desktop publishing, repairing wheelchairs and producing traffic signs, but such opportunities are not widely available, and many prisoners who work perform routine prison maintenance tasks (such as in the prison kitchen) or obsolete unskilled assembly work (such as in the prison laundry) that is argued to be no preparation for work after release. Classic 20th-century American prisoner work involved making license plates; the task is still being performed by inmates in certain areas.

Many businesses, large and small, already make use of prison workshops to produce high quality goods and services and do so profitably. They are not only investing in prisons but in the future of their companies and the country as a whole. I urge others to follow their lead and seize the opportunity that working prisons offer.