Subpoena, a judicial process directed to a witness commanding him to appear at the court, to testify what he knows in the case therein described, under a certain penalty (sub poena) mentioned in the process. If the court wishes to examine any books or papers which are in possession of the witness, a clause is inserted bidding him to bring them with him; and the subpoena is thence called a subpoena duces tecum. The subpoena ought to be served upon the witness personally, for otherwise he cannot be proceeded against as for a contempt if he neglects to appear. Service may be made by any person, and is proved generally by affidavit, or, if it be made by a sheriff or his officer, by a simple return or certificate of service. When a witness has been duly summoned, and his fees have been paid or tendered, or payment or tender has been waived, he is guilty of a contempt of court if he fails to appear at the appointed time, and may be proceeded against by attachment, for the double purpose of compelling him to appear and testify, and of vindicating the dignity of the court by the infliction of suitable punishment.

The party actually injured by the non-appearance may also have an action for all damages caused by his default. - The office of the subpoena at common law is simply to bring into court a witness whose evidence is sought. Chancery, borrowing the name of the writ, but giving it a far larger scope, issued it in order to compel a defendant in a cause to appear and answer upon oath the plaintiff's allegations. This process in chancery answers to a summons in the courts at law, and is the process by means of which the defendant is constructively brought before the court.