Persons who are deprived of their liberty (held in jail, prison, or a psychiatric institution) have the right to challenge the legality of their arrest or detention through a judicial inquiry or process known as habeas corpus. Habeas corpus is a centuries-old Latin phrase meaning “produce the body.” By means of a writ of habeas corpus, a court or judge may order the state to “produce the body”—in other words, to hand over the prisoner—so the court may review the legality of the prisoner’s detention.

For example, federal courts may use the writ of habeas corpus to determine if a state’s detention of a prisoner or other detainee—such as an institutionalized psychiatric patient—is lawful. A petition for writ of habeas corpus proceeds as a civil action against the state agent who is holding the prisoner in custody—usually a prison warden or psychiatric facility and treating psychiatrist.

State and federal prisoners often file a petition for writ of habeas corpus after their conviction to challenge the legality of federal laws that resulted in their detention. Habeas corpus petitions may also be used to challenge detention in immigration or deportation cases and military court detentions and convictions. And a habeas petition may be used to challenge preliminary matters in criminal prosecutions, such as (1) whether there is an adequate basis for detention; (2) removal to another federal district court; (3) the denial of bail or parole, or excessive bail; (4) the failure to provide for a speedy trial or hearing; (5) a claim of double jeopardy; (6) the legality of extradition to another state or a foreign country; or (7) the jurisdiction of the court. See 28 U.S.C. §2241.

Thus, the purpose of a writ of habeas corpus is not to determine the guilt or innocence of the detainee, but to test the legality of the current detention or confinement. It is a safeguard against imprisonment of persons detained in violation of the law—by requiring government authorities to provide valid reasons for the detention. If the habeas petition is granted and the writ is issued, it provides immediate relief from the unlawful detention by ordering the detainee be released from custody.

The right to petition for a writ of habeas corpus is guaranteed by the United States Constitution and by state constitutions.

In New York, as in other states, individuals who are detained in jail, prison, or a psychiatric institution have the right to challenge the legality of their detention through a judicial process known as habeas corpus. This right is protected by both the United States Constitution and the New York State Constitution. A writ of habeas corpus is a court order that commands the state to bring the detained individual before the court to determine if their detention is lawful. This process can be used to address issues such as the basis for detention, bail or parole decisions, speedy trial concerns, double jeopardy claims, extradition legality, and jurisdictional questions. The federal statute governing habeas corpus is 28 U.S.C. §2241, which outlines the scope and procedure for federal courts to review the legality of a state's detention of a prisoner. In New York, individuals or their attorneys can file a petition for a writ of habeas corpus after a conviction to challenge the legality of the detention, not to determine guilt or innocence. If the court grants the petition and issues the writ, it may result in the release of the detainee if the detention is found to be unlawful.