Hornor v. Henning et al. was a United States Supreme Court case that addressed the issue of whether a state court had the authority to issue a writ of mandamus to a federal court. The case involved a dispute between two parties, Hornor and Henning, over a contract for the sale of a steamboat. Hornor had filed a bill in the Circuit Court of the United States for the District of Maryland, seeking to enforce the contract. Henning then filed a petition in the Maryland Court of Appeals, asking the court to issue a writ of mandamus to the federal court, directing it to dismiss Hornor's bill. The Supreme Court held that the state court did not have the authority to issue a writ of mandamus to a federal court. The Court reasoned that the state court lacked jurisdiction over the federal court, and that the writ of mandamus was an extraordinary remedy that could not be used to control the proceedings of a court of another jurisdiction. The Court concluded that the state court had no authority to issue the writ of mandamus, and that the Circuit Court of the United States had jurisdiction to decide the case.

Justice Field delivered the dissenting opinion in Hornor v. Henning et al., arguing that the majority's decision was wrongfully based on a misapplication of state law. He argued that under Virginia law, which governed this case, an executor could not be held liable for debts incurred by his predecessor unless he had expressly assumed them or otherwise made himself responsible for them. In this case, there was no evidence to suggest that the current executor had done either of these things and thus should not have been held liable for any debt incurred by his predecessor. Justice Field further argued that even if it were possible to hold him accountable under Virginia law, it would still be inappropriate because he did not receive any benefit from those debts and therefore should not suffer any loss as a result of them either. Finally, Justice Field noted that while it may seem unfair to allow someone who has inherited an estate with outstanding debts to avoid responsibility for those obligations without making some sort of payment towards them; such is often necessary in order to protect innocent third parties who are owed money but cannot collect due to legal technicalities beyond their control.