The defendant in a lawsuit must be served (delivered) a summons or citation (an order from the court to appear and answer the lawsuit) and a copy of the lawsuit (1) to provide due process (fairness) by giving the defendant notice of the lawsuit and the opportunity to appear in court and defend the lawsuit; and (2) to give the court personal jurisdiction (authority) over the defendant.

In New Hampshire, as in other states, the legal process requires that a defendant in a lawsuit be properly served with a summons and a copy of the complaint. This is to ensure due process, which is the constitutional right to be informed of legal action against you and to have a fair opportunity to respond and defend yourself in court. The summons notifies the defendant that they are being sued and includes instructions on how to respond to the lawsuit. Serving these documents also allows the court to establish personal jurisdiction over the defendant, which means the court has the authority to make decisions regarding the defendant in the case. New Hampshire's rules regarding service of process are outlined in the New Hampshire Rules of Civil Procedure, specifically Rule 4. Service must be made by delivering a copy of the summons and complaint to the defendant personally, leaving it at the defendant's dwelling or usual place of abode with someone of suitable age and discretion residing therein, or by mailing it to the defendant's last known address by certified mail, return receipt requested. If service cannot be made by these means, the court may allow service by publication or other means.