The Due Process clauses of the United States Constitution prohibit courts from hearing a case that could adversely affect a party's interest unless that party has been given proper notice. To satisfy this notice requirement, notice must be reasonably calculated, under the circumstances, to inform all interested parties that a lawsuit is pending and that it could adverse affect their interests.
The degree of required notice varies depending on what type of jurisdiction a court intends to exercise. To exercise in personam jurisdiction, in-hand service of process is usually required. For in rem actions, which can affect the interests of anyone in the world, the plaintiff usually must inform all known parties of interest by a reasonably reliable means, and may then inform the rest of the world by "notice by publication" - purchasing a notice in a local newspaper multiple times over a period of several weeks. In tricky cases, courts work with plaintiffs to identify the best way of meeting notice requirements.
Notice is not a mere formality, as the Supreme Court recently discussed in Jones v. Flowers. In Jones v. Flowers, a state seized and sold property for unpaid property taxes. A certified letter meant to notify the owner of the impending sale was returned to the state as "unclaimed." Afterwards, the state made no additional attempt to contact the owner directly. The Court rejected the state's notice as insufficient, emphasizing that notice “must be such as one desirous of actually informing the absentee might reasonably adopt to accomplish it."
Because of the constitutional importance of insuring proper notice, courts will not forgive improper notice even where a party receives actual notice.