A debtors' prison is a prison for people who are unable to pay debt. Until the mid-19th century, debtors' prisons (usually similar in form to locked workhouses) were a common way to deal with unpaid debt in Western Europe. Destitute people who were unable to pay a court-ordered judgment would be incarcerated in these prisons until they had worked off their debt via labour or secured outside funds to pay the balance. The product of their labour went towards both the costs of their incarceration and their accrued debt. Increasing access and lenience throughout the history of bankruptcy law have made prison terms for unaggravated indigence obsolete over most of the world.

Since the late 20th century, the term debtors' prison has also sometimes been applied by critics to criminal justice systems in which a court can sentence someone to prison over willfully unpaid criminal fees, usually following the order of a judge. For example, in some jurisdictions within the United States, people can be held in contempt of court and jailed after willful non-payment of child support, garnishments, confiscations, fines, or back taxes. Additionally, though properly served civil duties over private debts in nations such as the United States will merely result in a default judgment being rendered in absentia if the defendant willfully declines to appear by law, a substantial number of indigent debtors are legally incarcerated for the crime of failing to appear at civil debt proceedings as ordered by a judge. In this case, the crime is not indigence, but disobeying the judge's order to appear before the court. Critics argue that the "willful" terminology is subject to individual mens rea determination by a judge, rather than statute, and that since this presents the potential for judges to incarcerate legitimately indigent individuals, it amounts to a de facto "debtors' prison" system.

In Canada, failure to pay a criminal fine in full by the due date results in "imprisonment in default" for a term calculated by dividing the debt (the fine plus the costs and charges of committing and conveying the defaulter to prison) by 8 hours per day at the minimum wage. For civil debts in British Columbia, a debtor may be jailed in contempt of court for defaulting on a required payment, and time spent in prison does not offset the debt.

During Europe's Middle Ages, debtors, both men and women, were locked up together in a single, large cell until their families paid their debt. Debt prisoners often died of diseases contracted from others interned in debtors' prison for many years. Some debt prisoners were released to become serfs or indentured servants (debt bondage) until they paid off their debt in labor.

Imprisonment for debt was also practised in Islam. Debtors who refused to pay their debts could be detained for several months in order to exert pressure on them. If they proved insolvent, they were released before being placed under legal guardianship.

Article 1 of Protocol 4 of the European Convention on Human Rights prohibits the imprisonment of people for breach of a contract. Turkey has signed but never ratified Protocol 4.

Debtor's prison, both for private and State debt, was common in Ancien Régime France. It was suppressed during the French Revolution (1793–1797), but later reinstated. The debtor's prison for civil debts was abolished in 1867.

France still allows for contrainte judiciaire, ordered by a judge, for persons unwilling to pay court-ordered fines as part of a judicial sentence. Older, underage and unsolvable persons are exempted from the contrainte. Though France has a rule that no definite proof is required to prove someone guilty of something but a set of proof, thus it’s only required that it’s likely someone is willfully not paying his fine rather than having to prove what exact money he does own (legally named revenues occultes), this can lead to someone insolvent being sentenced for being unable to pay his fine as soon as a small mismatch exists between the money being spent and the money on the tax return.