An Illinois Subpoena is a legal document issued by a court or other legal authority in the state of Illinois. It is a written order requiring a person to appear in court as a witness or to produce documents or other tangible evidence. There are two types of Illinois Subpoena: Subpoena Ducks Cecum and Subpoena Ad Testificandum. A Subpoena Ducks Cecum is a document ordering a witness to produce documents, records, or other tangible evidence for use in a legal proceeding. A Subpoena Ad Testificandum is a document ordering a witness to appear in court to testify.