A subpoena to testify at a deposition in a criminal case is a court order to appear and testify under oath in a criminal investigation. It is issued by the court or a representative of the court, usually at the request of either the prosecutor or the defense attorney. There are two types of subpoenas to testify at a deposition in a criminal case. The first type is a subpoena ad testificandum, which summons an individual to appear and testify in person. The second type is a subpoena duces tecum, which orders an individual to produce documents or other tangible evidence for use in the deposition.