In American criminal law, a material witness is a person with information alleged to be material concerning a criminal proceeding. The authority to detain material witnesses dates to the First Judiciary Act of 1789, but the Bail Reform Act of 1984 most recently amended the text of the statute, and it is now codified at 18 U.S.C. § 3144. The most recent version allows material witnesses to be held to ensure the giving of their testimony in criminal proceedings or to a grand jury.