Detention, often called imprisonment or being held in custody, is the state-authorized deprivation of a person's liberty. It is ordinarily executed by organs of the state such as the police or correctional authorities. For an arrest or continued detention to be lawful, it is typically founded on a criminal allegation, statutory authority, or a judicial order. When persons are deprived of liberty without legal basis, that practice is described as arbitrary detention and is internationally condemned.

Common forms and characteristics

Detention appears in several forms, each with different purposes and legal controls:

  • Pretrial or remand detention — custody while a person awaits charge, hearing or trial.
  • Post-conviction imprisonment — deprivation of liberty following a criminal conviction and sentence.
  • Administrative detention — custody for non-criminal reasons, such as immigration control or national security measures.
  • Alternative measures — supervised release, bail, electronic monitoring or house arrest as substitutes for full physical custody.

The legality of detention is constrained by national laws and international human-rights instruments. Key protections include the right not to be arbitrarily detained, prompt information about charges, access to legal counsel, the right to challenge detention before a court (habeas corpus or equivalent), and a speedy and fair trial. International instruments that address these protections include the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights. Detention should be carried out under state authority, for example by the state or government and commonly by the police, and it is normally justified only where there is a basis such as a criminal complaint or evidence of wrongdoing (criminal allegation).

Even lawful detention triggers obligations to preserve the dignity and physical integrity of detainees. The prohibition of torture and cruel, inhuman or degrading treatment is absolute; relevant standards are set out in instruments such as the Convention against Torture. International and domestic oversight mechanisms monitor conditions, length of detention, use of solitary confinement, and access to health care and legal advice.

Detention serves multiple social and legal functions: securing a suspect's appearance in court, protecting public safety, punishing wrongdoing after conviction, and in some systems temporarily removing persons considered a danger. However, detention is also a frequent subject of controversy: concerns include overcrowding, discrimination, prolonged pretrial detention, detention of migrants, and the risk of arbitrary or politically-motivated confinement.

Understanding detention requires attention to both formal rules and practical conditions. Judges, lawyers, human-rights bodies, and civil society often focus on reducing unnecessary use of custody, expanding alternatives to imprisonment, and ensuring procedural safeguards so that deprivation of liberty remains a lawful, proportionate and humane measure.