An Illinois Subpoena For Deposition is a legal document issued by the court that requires a witness to appear and give testimony during a deposition. This document is used in civil and criminal cases to compel a witness to appear in court and answer questions under oath. There are two types of Illinois Subpoena For Deposition: Subpoena Ducks Cecum and Subpoena Ad Testificandum. Subpoena Ducks Cecum requires the person being subpoenaed to bring documents or other physical evidence to the deposition while Subpoena Ad Testificandum requires the person to appear only to testify. Both types of subpoenas must be served on the witness in person or by certified mail.