Gay v. Alter 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 a federal prison. The case arose when a prisoner, John Gay, was held in a federal prison in the state of Pennsylvania. Gay sought a writ of habeas corpus from the state court, arguing that he was being held in violation of the Constitution. The state court granted the writ, and the federal government appealed 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 power, 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 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 power, 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 interfere with the federal government's power to protect this right.

Justice Field delivered the dissenting opinion in Gay v. Alter, arguing that the court should not have granted a writ of error to review the decision of the Supreme Court of California. He argued that there was no federal question involved and thus it did not fall within this court's jurisdiction. Furthermore, he noted that even if there were a federal question present, it had already been decided by both state courts and therefore could not be reviewed again by this court. Finally, Justice Field argued that since Congress had given exclusive jurisdiction over patent cases to district courts rather than circuit courts or supreme courts, any questions regarding patents should also be left for those lower tribunals to decide instead of being heard here at this level.