Any one of several common-law writs, which issue out of a court of justice, or (in England) are awarded by a judge in vacation, and require the body of a person to be brought before the judge or into the court for some purpose specified in the writ.

The name arises from the emphatic words habeas corpus ('have the body') which occur in the writs so called. In the broadest inclusion, besides the writs now commonly so called, the writ known as capias is covered by the term habeas corpus, and these words form a part of the Latin form of the writ. Of all these writs the one which is now of primary importance, and which is commonly meant by the term, is that of which the fuller name is habeas corpus ad subjiciendum, the history and law concerning which is here briefly stated under that fuller name. Other writs of minor importance are given below under their fuller names, by which they are ordinarily distinguished.

Habeas Corpus ad Subjiciendum

This is a prerogative writ requiring the body of a person alleged to be unlawfully restrained of liberty to be brought before the judge or into court, that the lawfulness of the restraint may be investigated and determined. The writ is addressed to the person in whose custody the detained person is alleged to be, and commands him to produce the body of the prisoner before the court and there state the cause and warrant for his detention, or show cause why this was not done.

At the time when the Magna Charta declared that no "freeman may be taken or imprisoned but by the lawful judgment of his peers or by the law of the land," there seems to have been no definite machinery available by which a freeman so imprisoned could recover his freedom. This was due partly to the fact that the power was not then fully centralized, partly to the fact that the King's court (through which this was then to be accomplished if at all) was not yet ready to set at naught the King's will, and partly that the law seemed to fear too little rather than too much imprisonment of malefactors, and the action for false imprisonment seemed a sufficient check for merely lawless confinement. The words 'habeas corpus' are making their way into various writs, but they are not yet habitually used of any method of investigating the cause or legality of an imprisonment.

A person arrested was set free as soon as some sureties became bound for his appearance in court. It was not common to keep men in prison, not (apparently) because of any love of the abstract idea of liberty, but because imprisonment was costly and troublesome to the sheriff. The sheriff enjoyed a discretionary power of detaining or releasing prisoners upon sureties such as he considered sufficient, except that he might not set at liberty any one imprisoned by the special command of the King. A writ (de homine replegiando), which came into currency during this same period, directed the sheriff to deliver the prisoner unless he were taken at the special command of the King or his chief justiciar or for the death of a man, or for some forest offense, or for some other cause which by law made him irrepleviable; but the writ was so worded as to throw upon the sheriff the responsibility of deciding whether the prisoner should be kept in custody.

In theory the central court (King's Court) had a control over the entire province of criminal justice, and at times directed a sheriff to send prisoners to Westminster for trial; but such instances at this date were rare, and were generally from Chancery rather than from the justices, and were more governmental than judicial in their origin. Undoubtedly, also, if a man thought himself unlawfully imprisoned by the sheriff or by some lord of a franchise, and made himself heard in the King's Court, the justices of that court had power to order that his body be brought before them, a nd to liberate him if persuaded that his imprisonment was unlawful.

Although in 1234 the royal court, by the mouth of William Raleigh, declared null and void the outlawry of Hubert de Burgh, which the King had especially commanded, this victory of law over arbitrary power was gained only after a revolt and a change of Ministry. In spit of this, a man committed to jail by the 'mandate of the King' would have found none to liberate him. It was two hundred years before the habeas corpus as the appropriate instrument for enforcing the law of personal liberty granted by Magna Charta became well established, and it was not until the reign of Charles II, that the last vestige of the superiority of the King's mandate disappears.

In Darnel's case (3 Charles I., 1627) the judges declared that a return to a writ of habeas corpus directed to the warden of the Fleet Prison, which set forth that the prisoner was detained by warrant of the Privy Council, was a sufficient answer to the writ. The result of the indignation consequent upon this subserviency of the judges to the King's will was the passage of the Petition of Right (16 Charles I., ch. 10, sec. 8), which provided that the writ of habeas corpus should be granted as of course to a person committed by the King or Privy Council upon demand made to the Court of King's Bench or Common Pleas, thus extending the power of granting the writ to the Common Pleas Court by statute.

In 1676 the court refused to grant a writ upon such a motion in vacation, and this resulted in the passing of the Habeas Corpus Act. The substance of the act is that the sheriff or other person having a prisoner in his custody shall, when a writ of habeas corpus is directed to him, bring the body of his prisoner into court, within a time fixed, with the true cause of his detainer or imprisonment, unless the commitment was for treason or felony plainly expressed in the warrant; that the writ of habeas corpus should be granted in vacation time by the Lord Chancellor, the writ to be returnable immediately and the prisoner to be discharged on giving security for his appearance before the proper court, except in case of persons committed for treason or felony expressed in the warrant of commitment, persons convicted or suffering execution by legal process, and persons detained upon a legal process or for an offense not bailable upon a justice's warrant; that persons discharged on habeas corpus shall not be recommitted for the same offense except by the court having cognizance of the case; persons committed to prison for treason or felony if not indicted and tried in or before the second term or session after commitment should be discharged; and that no inhabitant of England (except convicted felons and those contracting to be transported) shall be sent as prisoners to Scotland, Ireland, Jersey, etc., or any place beyond the seas. Stringent penalties provided for a forfeit of £500 against a judge delaying the issue of the writ, costs and damages of not less than £500, besides the penalties of praemunire for illegal transportation beyond seas.