Habeas Corpus, literally (from Latin) “(We command) that you have the body”. This is an important legal tool to defend oneself against arbitrary or unlawful arrest. Habeas Corpus is a legal action undertaken to seek relief from arbitrary or unlawful arrest, either by the person arrested him or herself, or by a representative. The court should then issue a writ (a writ is a formal written order issued by a court) ordering the custodian, i.e. the person or institution imprisoning a person, to bring this person to the court so that the court can determine whether the custodian has lawful authority to hold the person. If not, the person should be released from custody.
Any prisoner, in a well functioning judicial system, may petition the courts or individual judges for a writ of Habeas Corpus. (A petition is a request to an authority, more specifically in this case it is a legal pleading that initiates a case to be heard before a court. The purpose of a pleading is a correction or repair of some form of injustice, e.g. arbitrary arrest).
Habeas Corpus does not determine guilt or innocence, merely whether the person is legally imprisoned or not. It can also be a writ against a private individual detaining another, for example in slavery.
It has historically been and still remains today an important tool for safeguarding of individual freedom against arbitrary state action. Currently, the U.S. is trying to set very strict limits to the writ, limits previously unheard of in democratic societies. The current U.S. administration believes restrictions on Habeas Corpus are necessary in the war on terrorism.
Article 9 of the Universal Declaration of Human Rights states that “No one shall be subjected to arbitrary arrest, detention or exile”. One can therefore claim that the writ is an important means to make this right real.