Carper v. Fitzgerald was a United States Supreme Court case that addressed the issue of whether a state court could issue a writ of habeas corpus to a prisoner who was being held in federal custody. The case arose when the petitioner, Carper, was arrested and charged with a federal crime in the District of Columbia. He was then transferred to a federal prison in Maryland. Carper then filed a petition for a writ of habeas corpus in the state court of Maryland, seeking to be released from federal custody. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus is a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to detain a prisoner. The Court also noted that the writ of habeas corpus is a remedy that is available only to those who are held in state custody, and not to those held in federal custody. The Court's decision in Carper v. Fitzgerald established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal custody. This decision has been cited in numerous subsequent cases, and has been used to support the principle that the federal government has exclusive authority over the detention of federal prisoners.

In Carper v. Fitzgerald, the Supreme Court was tasked with determining whether a state court had jurisdiction to hear an appeal from a federal district court's decision in a case involving land titles. The majority opinion held that the state court did not have jurisdiction and that only the United States Circuit Court of Appeals could review such decisions. Justice Field dissented, arguing that Congress had given states authority to determine title disputes over public lands within their borders and thus it was reasonable for them to be able to hear appeals regarding those matters as well. He further argued that since there were no laws preventing states from hearing these cases, they should be allowed to do so unless expressly prohibited by Congress or other governing bodies. In conclusion, he believed that allowing state courts access would provide more efficient resolution of these types of cases without infringing on any rights granted by federal law or otherwise violating constitutional principles.