Blair v. Gray 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 who was being held in a federal prison. The case arose when a prisoner, William Blair, was held in a federal prison in the state of Virginia. Blair 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 remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals. The Court also noted that the writ of habeas corpus was a remedy that could only be used to challenge the legality of a person's detention, and not to challenge the conditions of the detention. The Court's decision in Blair v. Gray established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal prisons. This decision has been cited in numerous subsequent cases, and has been used to support the principle that state courts cannot interfere with the federal government's authority to imprison individuals.

Justice Field delivered the dissenting opinion in Blair v. Gray, arguing that the majority's decision was wrongfully based on a misinterpretation of the law and facts of the case. He argued that under Missouri state law, which governed this dispute, only one party could be held liable for an injury caused by a defective product - either its manufacturer or seller - not both as determined by the majority. Furthermore, he noted that there was no evidence to suggest any negligence on behalf of Gray; rather it appeared to him that all liability should rest with Blair alone since he had manufactured and sold an inherently dangerous product without warning customers about its potential risks. Finally, Justice Field concluded his dissent by noting how unfair it would be if two parties were held responsible for damages when only one was actually at fault.