Ex parte Perry is a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The case arose when a prisoner, William Perry, was held in federal custody in the state of Texas. Perry sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. The federal government argued that the state court did not have the authority to issue such a writ, as the power to issue writs of habeas corpus was reserved to the federal government. The Supreme Court ultimately 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 power to issue writs of habeas corpus was a power reserved to the federal government, and that the state court did not have the authority to interfere with the federal government's power. The Court also noted that the state court's writ of habeas corpus would have interfered with the federal government's power to enforce the laws of the United States. As such, the 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.

In Ex Parte Perry, the Supreme Court was asked to determine whether a state court had jurisdiction over an appeal from a federal district court. The majority opinion held that it did not have such jurisdiction because the case involved matters of federal law and thus should be heard in a higher federal court. Justice Field dissented, arguing that states have concurrent jurisdiction with the United States when it comes to appeals from lower courts. He argued that this is especially true for cases involving questions of fact rather than questions of law, as was the case here. Furthermore, he noted that Congress has granted state courts authority to hear certain types of appeals from lower federal courts and there is no reason why they cannot do so in other cases as well if both parties agree upon it. In conclusion, Justice Field believed that allowing state courts to exercise their concurrent jurisdiction would promote justice by providing more options for litigants seeking relief on appeal without having to go through lengthy delays or additional expense associated with appealing directly up through multiple levels of higher federal courts