[Latin, In the thing itself.] A lawsuit against an item of property, not against a person (in personam).
An action in rem is a proceeding that takes no notice of the owner of the property but determines rights in the property that are conclusive against all the world. For example, an action to determine whether certain property illegally imported into the United States ought to be forfeited can be captioned United States v. Thirty-nine Thousand One Hundred and Fifty Cigars. The object of the lawsuit is to determine the disposition of the property, regardless of who the owner is or who else might have an interest in it. Interested parties might appear and make out a case one way or another, but the action is in rem, against the things.
In rem lawsuits can be brought against the property of debtors in order to collect what is owed, and they are begun for the partition of real property, foreclosure of mortgages, and the enforcement of liens. They may be directed against real or personal property. In rem actions are permitted only when the court has control of the property or where its authority extends to cover it. For example, the courts in Kansas may determine rights to a farm in Kansas, but not the ownership of a cannery in Texas. The in rem jurisdiction of a court may be exercised only after parties who are known to have an interest in the property are notified of the proceedings and have been given a chance to present their claim to the court.