An order issued under the authority of a court (but signed by a lawyer) directing a person or legal entity to produce evidence in a matter, including documents and testimony (A subpoena ducus tecum) or to testify (subpoena ad testificandum). Subpoenas are usually directed to third parties to the litigation. The term subpoena is primarily US usage. It is in principle possible in most jurisdictions to seek orders to third parties to produce evidence relevant to a court proceedings, but there tend to be more procedural safeguards than in US practice, based on the view that a non-party to a legal proceeding ought not to be troubled or harassed in another party’s case.
In US practice any lawyer admitted to the Federal Courts can usually issue a subpoena out of any US District Court where the target of the subpoena resides and for a certain distance from that court; by simply filling in a standard subpoena form – which then must be opposed. US courts cannot issue effective subpoenas to parties outside the United States – so evidence from such parties must be gathered using the Hague Convention on the Taking of Evidence Abroad in Civil or Commercial Matters. By contrast, the English courts require a party to apply to the court for third party discovery. but must show that (i) the documents are likely to support its case or adversely affect the case of another party in the proceedings, and that (b) disclosure is necessary for a fair hearing of the claim or to reduce costs (usually by bringing the case to an early conclusion.) Non-US lawyers often find the ease with which a subpoena can be issued startling (though they often have the same reaction to the scope of US Discovery.)
If a US subpoena is improperly issued, or genuinely burdensom, the target of the subpoena can apply to have the subpoena “quashed,” but may incur legals costs doing so.
A subpoena is not always a hostile act – it might be desired by the subpoena’d party so as to overcome the restrictions imposed by for example a non-disclosure agreement or in a legal settlement, or under the rules of an organisation they are a member of. Indeed, counsel for the party to receive the subpoena may even negotiate its language, while agreeing not to oppose. This is often referred to as a ‘friendly subpoena.’