Being a witness in court is often difficult and overwhelming. If you are under subpoena to appear as a witness you have a lawful obligation to attend, unless you are released by the party who issued the subpoeana. Most commonly, the Crown Prosecutor will be the one issuing subpoenas for witnesses at criminal trials. If you do not attend and are not excused, the presiding judge may issue a warrant for your arrest (called a witness warrant). You could be arrested and may have to explain to a different judge why you failed or refused to attend court.