A subpoena is used to compel the testimony of witnesses in a trial or other adversarial proceeding. Subpoenas are issued by the clerk of the court (see below) in the name of the judge presiding over the case in which the witness is to testify. (Additionally, court rules often permit lawyers to issue subpoenas themselves in their capacity as officers of the court.) Typically subpoenas are issued "in blank" and it is the responsibility of the lawyer representing the plaintiff or defendant on whose behalf the testimony is to be given to serve the subpoena on the witness.
The subpoena will usually be on the letterhead of the court where the case is lodged, naming the parties to the case, and being addressed by name to the person whose testimony is being sought. It will contain the language "You are hereby commanded to report in person to the clerk of this court" or similar, describing the specific location and scheduled date and time of the appearance. Some issuing jurisdictions include an admonishment advising the subject of the criminal penalty for failure to comply with a subpoena, and reminding him or her not to leave the court facilities until excused by a competent authority.
The subpoena has its source in English common law and it is now used almost with universal application throughout the Anglo-American common law world. However, for Civil proceedings in England and Wales, the term has been replaced by witness summons, as part of reforms to replace Latin terms with easier to understand English terms