A subpoena and a summons are similar because they both are used to give notice about a court proceeding. A summons is an official notice of a lawsuit. It used to give notice to a person that they are being sued and that they need to appear in court to fight the lawsuit. A subpoena on the other hand, is a court order. A subpoena requires a person to come to court, go to a deposition, or give documents or evidence. A subpoena like a summons must be served to the individual that it is for.