Subpoena Ad Testificandum

A subpoena ad testificandum (Latin: "subpoena to testify") is one of two classical forms of subpoena in common-law systems, the other being the subpoena duces tecum, which compels the production of documents or tangible evidence. Where the duces tecum targets things, the ad testificandum targets a person's live testimony.

The instrument originated in English chancery practice and is now codified across common-law jurisdictions. In the United States, federal courts issue them under Rule 45 of the Federal Rules of Civil Procedure and Rule 17 of the Federal Rules of Criminal Procedure. Congressional committees possess analogous compulsory process derived from Article I and recognized by the Supreme Court in McGrain v. Daugherty (1927) and Watkins v. United States (1957). In the United Kingdom, the equivalent is now styled a "witness summons" under the Civil Procedure Rules 1998.

A valid subpoena ad testificandum typically must:

• Identify the witness by name and the issuing authority;
• Specify time, date, and place of appearance;
• Be served personally within the court's territorial jurisdiction, often with a witness fee tendered;
• Allow reasonable time for compliance.

Failure to obey, absent a successful motion to quash, can result in civil or criminal contempt. Recognized defenses and privileges include the Fifth Amendment privilege against self-incrimination, attorney-client privilege, spousal privilege, and, in limited cases, executive privilege — the latter at the center of United States v. Nixon (1974), in which the Supreme Court enforced a trial subpoena against the President.

For researchers and MUN delegates, the doctrine matters chiefly because legislative oversight investigations — whether by the U.S. Congress, the UK Parliament's select committees, or commissions of inquiry — rely on this compulsory power to secure testimony from officials, executives, and foreign nationals present within jurisdiction. International tribunals such as the ICC and ICTY employ functionally similar mechanisms under their statutes (e.g., ICC Statute Article 64), though enforcement depends on state cooperation rather than direct contempt power.