Thornington v. Smith was 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 a federal prison. The case arose when a prisoner, Thornington, was held in a federal prison in the state of Maryland. Thornington sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. 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 a federal prison. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's power to protect this right. In conclusion, 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 a federal prison. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's power to protect this right.

In Thorington v. Smith, 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 diversity of citizenship. The majority opinion held that the state court did not have such jurisdiction and thus could not hear the appeal. However, Justice Field dissented on this point, arguing that under Article III of the Constitution, Congress has exclusive authority over appeals from federal courts to state courts when there is diversity of citizenship among parties involved in litigation. He argued further that Congress had exercised its power by passing statutes granting appellate jurisdiction to certain states' highest courts for cases where there is diversity between citizens of different states or countries. Therefore, he concluded that it was within Congress' power to grant such appellate jurisdiction and consequently within those particular states' powers as well to exercise it - meaning they were able to hear appeals from decisions made by federal district courts when there is diversity between citizens involved in litigation.