Jurisdiction in rem (Latin, power about or against "the thing") is a legal term describing the power a court may exercise over property (either real or personal) or a "status" against a person over whom the court does not have "in personam jurisdiction". Jurisdiction in rem assumes the property or status is the primary object of the action, rather than personal liabilities not necessarily associated with the property (quasi in rem jurisdiction).
Within the US federal court system, jurisdiction in rem typically refers to the power a federal court may exercise over large items of moveable property, or real property, located within the court's jurisdiction. The most frequent circumstance in which this occurs in the Anglo-American legal system is when a suit is brought in admiralty law against a vessel to satisfy debts arising from the operation or use of the vessel. However, it can involve other things, such as Margaret Sanger's Japanese pessaries in United States v. One Package of Japanese Pessaries, an important case in United States reproductive and obscenity law. Another example of jurisdiction in rem was the United States v. Forty Barrels and Twenty Kegs of Coca-Cola.
Within the US state court system, jurisdiction in rem may refer to the power the state court may exercise over real property or personal property or a person's marital status. State courts have the power to determine legal ownership of any real or personal property within the state's boundaries.
A right in rem or a judgment in rem binds the world as opposed to rights and judgments inter partes which only bind those involved in their creation.
Originally, the notion of in rem jurisdiction arose in situations in which property was identified but the owner was unknown. Courts fell into the practice of styling a case not as "John Doe, Unknown owner of (Property)", but as just "Ex Parte (property)" or perhaps the awkward "State v. (Property)", usually followed by a notice by publication seeking claimants to title to the property. This last style is awkward because in law, only a person may be a party to a judicial proceeding, and a non-person would at least have to have a guardian appointed to represent its interests, or the interests of the unknown owner.
The use of this kind of jurisdiction in asset forfeiture cases is troublesome because it has been increasingly used in situations where the party in possession is known, which by historical common law standards would make him the presumptive owner, and yet the prosecution and court presumes he is not the owner and proceeds accordingly. This kind of process has been used to seize large sums of cash from persons who are presumed to have obtained the money unlawfully because of the large amount, often in situations where the person could prove he was in lawful possession of it, but was forced to spend more on legal fees to do so than the amount of money forfeited.