The writ of habeas corpus, sometimes called "the Great Writ," is one of the six prerogative writs  of the English common law. Now embodied in statutes in the U.S., habeas is an individual's protection from unlawful imprisonment. When we say "habeas corpus" nowadays we mean what was actually "habeas corpus ad subjiciendum" -- there used to be a lot of similar writs  for bringing a prisoner into court for various reasons (such as a trial or sentencing on other criminal charges), but the one most frequently seen today (and referred to by its full name) is the writ of habeas corpus ad testificandum, used to have guards bring a prisoner to court to (= ad) testify (= testificandum) as a witness in a lawsuit between other people.
A "writ" is simply a court order, and habeas corpus (Latin: "you should have the body") derives from the wording of the medieval writ, in which the court would order someone (now called "the respondent") to bring before it at the specified time and place a person (now called "the petitioner" because the document one files with the court, asking to be released from custody, is now called "a petition") the respondent was holding prisoner. If/when the respondent did show up with the petitioner as ordered, the court would hold a hearing (which is a trial without a jury) on whether keeping the petitioner incarcerated was lawful -- if so, the court would "quash" the writ (that is, cancel it), and the respondent would take the petitioner back to jail. If the court found the incarceration to be unlawful (what we call "unconstitutional"), however, the writ stood, and the petitioner was released right then and there. Thus what we call "the right" of habeas corpus is actually the right to petition for what we call today an "order to show cause," meaning that if the court does not deny the habeas petition, what the petitioner gets is a court hearing to decide whether keeping the petitioner locked up is unconstitutional.
The Anglo-Saxon common law in England before the Norman Conquest (1066) recognized the right not to be imprisoned unlawfully, but they did not use a Latin name for it, and it was one of the rights listed (for nobles, anyhow, which is what a "free man" was at that time) in Magna Carta , but that, too, was before the formal writ evolved that gave it its name. Nor is the right called habeas corpus in the civil-law systems of countries without the English common-law heritage, but they generally recognize it as a fundamental freedom, whatever they call it.
Habeas in the United States
The U.S. Constitution mentions habeas corpus only in Section 9 of Article I (which enumerates the powers of Congress) and only in the context of suspending the right in times of insurrection. This led to a confrontation between President Abraham Lincoln and the U.S. Supreme Court during the American Civil War (1861 - 1864), when Lincoln suspended the writ of habeas corpus, and the Chief Justice of the U.S. ruled that was unconstitutional, and Lincoln ignored him. The issue is whether the Constitution gives the President, or exclusively the Congress, authority to suspend habeas corpus, and the question has been raised again in connection with the "War on Terrorism," especially in litigation over the rights of prisoners held by the U.S. in Guatánamo Bay, Cuba.
Petitioning for habeas is a method many prison inmates use for seeking post-conviction relief, because if the habeas court rules the conviction was unconstitutional, the petitioner will either get a new trial or be cleared of the criminal charges entirely, and petitions for habeas are not subject to the same time limits as direct appeals from the criminal conviction, so they can be filed years after the criminal trial, if new evidence becomes available.
Because the due-process right habeas corpus protects is a federal civil right, guaranteed by the U.S. Constitution, a person convicted of a state crime in a state court, and held in a state prison, may petition a federal trial court (= a U.S. District Court) to review the constitutionality of that state conviction. Such a case is considered a civil suit (not a criminal case) in the federal court, and the petition usually names as respondent the warden of the state prison where the petitioner is being held. The federal statute governing habeas petitions by state prisoners is 28 U.S.C. §2254 (and 28 U.S.C. §2241 applies to habeas petitions by federal prisoners).
Lawyers who handle much habeas litigation usually do so in the larger context of practicing criminal-defense and/or civil-rights law, because habeas is a sub-field of the law, requiring specialized knowledge about the principles of habeas law as well as a good working knowledge of constitutional law and both criminal and civil procedure.
- The others are: certiorari, mandamus, procedendo, prohibito, and quo warranto. The six are sometimes called "extraordinary writs," and they are actually equitable remedies.
- Some others were: habeas corpus ad deliberandum et recipiendum; habeas corpus ad faciendum et recipiendum; habeas corpus ad prosequendum; habeas corpus ad recipiendum; habeas corpus ad respondendum; habeas corpus ad satisfaciendum; and habeas corpus cum causa.
- The clause usually numbered 39 in the 1215 text (and 29 in the version re-issued in 1225) says, "Nullus liber homo capiatur, vel imprisonetur, aut disseisiatur, aut utlagetur, aut exuletur, aut aliquo modo destruatur, nec super cum ibimus, nec super cum mittemus, nisi per legale judicium parium suorum vel per legem terre." The great English jurist Sir Edward Coke (1552 - 1634) translated it as: "No freeman shall be taken, or imprisoned, or be disseised of his freehold, or liberties, or free customs, or be outlawed, or exiled, or any otherwise destroyed; nor will we not pass upon him, nor condemn him, but by lawful judgment of his peers, or by the law of the land."
- That clause says, "The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it."
- Ex parte Merryman, 17 F. Cas. 144 (Circuit Court, Dist. Maryland, 1861).
- As opposed to an appeal of the conviction, which is a continuation of the criminal-trial process itself, a proceeding for post-conviction relief is a whole new legal case filed to have a court order an improvement in the situation of a person who was convicted of a crime. There are many common kinds of relief, and some of them (such as having the conviction invalidated because new evidence shows the convict did not commit the crime) are available only to a convict who was found guilty at a trial, while others (such as challenging the conditions of confinement because of prison over-crowding) are also available to persons who pled guilty and so waived having a trial.
Federal Habeas Corpus Statutes