Goodwin v. Fo 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, John Goodwin, was held in a federal prison in the state of New York. Goodwin sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. 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 Goodwin v. Fo 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 Goodwin v. Fo, arguing that the majority's decision was wrongfully based on a misreading of the contract between the parties. He argued that under California law, which governed this case, an agreement to pay for services rendered is not necessarily considered a debt and thus does not fall within the scope of bankruptcy proceedings. Furthermore, he noted that there had been no proof presented by either party as to whether or not such an agreement constituted a debt according to California law at all. As such, Justice Field concluded that it was improper for the Court to make any determination regarding this issue without first examining state law on this matter more closely and determining what constitutes a debt under those laws before making its ruling in favor of Fo over Goodwin.