Buchanan v. Smith was a United States Supreme Court case that addressed 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 Buchanan, was held in a federal prison in the state of Tennessee. The state court issued a writ of habeas corpus to the warden of the prison, ordering him to produce Buchanan before the court. The warden refused to comply with the writ, arguing that the state court did not have the authority to issue the writ because the prisoner was being held in a federal prison. The Supreme Court held that the state court did not have the authority to issue the writ of habeas corpus. The Court reasoned that the writ of habeas corpus was a federal remedy and that the state court did not have the authority to issue the writ in a case involving a federal prisoner. The Court also noted that the writ of habeas corpus was a remedy that was available only to federal prisoners and that the state court did not have the authority to issue the writ in a case involving a state prisoner. The Court's decision in Buchanan v. Smith established that state courts do not have the authority to issue writs of habeas corpus in cases involving federal prisoners. The decision also established that the writ of habeas corpus is a federal remedy and that state courts do not have the authority to issue the writ in cases involving state prisoners.

Justice Field delivered the dissenting opinion in Buchanan v. Smith, arguing that the majority's decision was incorrect and should be reversed. He argued that a state cannot constitutionally pass laws which interfere with or impair contracts made between individuals before such laws were passed. The contract at issue in this case was valid when it was entered into by both parties, and thus could not be impaired by any subsequent law of the State of New York. Furthermore, Justice Field noted that if states are allowed to pass laws which retroactively impair existing contracts, then no one would have any security for their contractual rights since they could always be changed or taken away without notice or compensation by a later act of legislature. As such, he concluded that allowing states to do so would violate Article I Section 10 Clause 1 of the United States Constitution prohibiting impairment of contracts and therefore reverse the judgment below as unconstitutional under federal law