The paper that tells a defendant that he or she is being sued and asserts the power of the court to hear and determine the case. A form of legal process that commands the defendant to appear before the court on a specific day and to answer the complaint made by the plaintiff.
The summons is the document that officially starts a lawsuit. It must be in a form prescribed by the law governing procedure in the court involved, and it must be properly served on, or delivered to, the defendant. If the prescribed formalities are not observed, the court lacks authority to hear the dispute.
In the federal district courts, the summons is prepared by the attorney for the plaintiff and given to the clerk of the court where the case will be heard. When the plaintiff's complaint, setting out his claim, is filed with the court, the clerk signs the summons and gives it and a copy of the complaint to a U.S. marshal or to someone else appointed to serve the papers. Once the summons and complaint are served on the defendant, she must respond to them within twenty days or whatever other time the court allows.
Some states follow this same procedure, but other states allow service of the summons and complaint by delivery directly to the defendant. In those states, the lawsuit is considered begun as soon as the defendant receives the papers,
even though nothing has yet been filed with a court. Actions commenced in this way are sometimes called "hip pocket" suits.