The Due Process clauses in the United States Constitution prohibit courts from exercising personal jurisdiction over a defendant unless the defendant has proper notice of the court's proceedings. To meet this rule, courts require plaintiffs to arrange for defendants to be served with a court summons and a copy of the plaintiffs' complaint.
The summons and complaint must be either given directly to defendants or left with a suitable person at their home or place of business. Service may usually be performed by any adult who is not a party to the lawsuit. Plaintiffs may hire professional process servers to serve defendants. See Rule 4 of the Federal Rules of Civil Procedure.