A subpoena (also subpœna) is a writ issued by a government agency, most often a court, to compel testimony by a witness or production of evidence under a penalty for failure. There are two common types of subpoena:

1. subpoena ad testificandum orders a person to testify before the ordering authority or face punishment. The subpoena can also request the testimony to be given by phone or in person.
2. subpoena duces tecum orders a person or organization to bring physical evidence before the ordering authority or face punishment. This is often used for requests to mail copies of documents to the requesting party or directly to court.