In common law , an order issued in the name of a sovereign or court commanding a person to perform or refrain from performing a specified act.
It was a vital official instrument in Old English law. A plaintiff would commence a suit by choosing the proper form of action and obtaining a writ appropriate to the remedy sought; its issuance forced the defendant to comply or to appear in court. Writs were also constantly in use for financial and political purposes of government. Though the writ no longer governs civil pleading and has lost many of its applications, the extraordinary writs, especially of habeas corpus , mandamus (commanding the performance of a ministerial act), prohibition (commanding an inferior court to stay within its jurisdiction), and certiorari , reflect its historical importance as an instrument of judicial authority.