subpoena [Lat.,=under penalty], in law, an order to a witness to appear before a court. A subpoena ad testificandum [Lat.,= to testify under penalty], the technical term denoting an ordinary subpoena, is a command for an individual to appear at a particular time and place to testify on a specific matter. A subpoena duces tecum [Lat.,=bring with you under penalty] requires a witness to produce at trial books, personal papers, or other material relevant to a judicial proceeding. Failure to obey a subpoena constitutes contempt of court, though subpoenas can be challenged.

In law, a writ commanding the person upon whom it has been served to appear in court or before a congressional committee, grand jury, or some other body, under a penalty for failure to comply. Unlike a summons, a subpoena may command the recipient to produce evidence necessary to the resolution of a legal matter or controversy.

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