Galpin v. Page 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 Galpin, was held in a federal prison in California. Galpin sought a writ of habeas corpus from the California Supreme Court, claiming that he was being held in violation of the Constitution. The California Supreme Court granted the writ, and the United States Supreme Court was asked to decide whether the state court had the authority to do so. 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 power to issue such a writ. 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 that the state court did not have the power to determine the legality of a federal detention. The Court's decision in Galpin v. Page established that state courts do not have the authority to issue writs of habeas corpus to challenge the legality of a federal detention. The decision also established that the writ of habeas corpus is a federal remedy, and that state courts do not have the power to issue such a writ.

Justice Field delivered the dissenting opinion in Galpin v. Page, arguing that the majority's decision was an incorrect interpretation of California law and would lead to unjust results. He argued that under California law, a mortgagee had no right to foreclose on mortgaged property unless it was done within one year after default or demand for payment. The majority held that this rule only applied when there were multiple mortgages on the same property; however, Justice Field disagreed with this interpretation because he believed it did not reflect what California courts had previously decided about such matters. Furthermore, he argued that if the majority's ruling stood as precedent then any mortgagee could wait indefinitely before seeking foreclosure without consequence - something which would be unfair to debtors who may have already paid off their debts but are still subject to foreclosure due to a delay by their creditors in filing suit against them. Ultimately, Justice Field concluded his dissent by stating his belief that "the court should never give its sanction"to interpretations of state laws which do not accurately reflect existing legal principles and will result in injustice for those affected by them.