Habeas corpus—also known as the Great Writ—is the legal procedure that prevents the federal government from arresting and holding (in prison) a person indefinitely without showing cause for detaining the person. This Latin term is pronounced "Hay-bee-us Corp-us."

A person detained by the federal government may challenge their detention by filing a habeas corpus petition—which then requires the government to explain to a neutral judge the justification for detaining the person. A habeas petition is prosecuted or litigated as a civil (noncriminal) matter against the government agent (usually the prison warden) who holds the defendant in custody.

The Founders of the United States who wrote the U.S. Constitution believed so strongly in this protection against government overreach they included it in the first article of the Constitution (Article I, Section 9, Clause 2).

In Louisiana (LA), as in all states, the principle of habeas corpus is a critical component of the legal system, providing a means to challenge unlawful detention. Habeas corpus, enshrined in Article I, Section 9, Clause 2 of the U.S. Constitution, is a federal right that applies to all states, including Louisiana. It allows a person held by the federal government to file a petition in court to question the legality of their detention. The government must then present a valid legal reason for the individual's imprisonment. In Louisiana, state statutes also provide for habeas corpus procedures, which are consistent with federal law. These procedures are typically outlined in the Louisiana Code of Criminal Procedure, allowing individuals detained by state authorities to similarly challenge their detention. The petition is filed against the government agent, usually the prison warden, responsible for the detainee's custody, and it is treated as a civil action, not a criminal one. The right to habeas corpus is a fundamental safeguard against arbitrary detention and ensures that the government's power to detain individuals is exercised within the bounds of the law.