Putnam v. Day 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, Putnam, was held in a federal prison in California. Putnam 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 Putnam v. Day 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.

In Putnam v. Day, the Supreme Court was asked to decide whether a contract between two parties could be enforced when one of the parties had died before it was fully executed. The majority opinion held that such contracts were not enforceable because they lacked consideration and mutuality of obligation. However, in his dissenting opinion Justice Field argued that this decision would lead to unjust results for innocent third-party beneficiaries who relied on these contracts being fulfilled as promised. He noted that if the deceased party had intended to perform their obligations under the contract then there should be no reason why those obligations cannot still be carried out by their estate or representatives after death. Furthermore, he argued that enforcing such contracts would provide an incentive for people to fulfill their promises even after death since any breach of promise could result in legal action against them or their estate by aggrieved third-parties who relied upon performance of those promises