Erhardt v. Boaro & Others 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, Erhardt, was held in a federal prison in California. Erhardt 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 Erhardt v. Boaro & Others 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 Erhardt v. Boaro & Others, the United States Supreme Court was tasked with deciding whether a contract between two parties should be enforced even though it had been made in violation of an existing state law. The majority opinion held that the contract could not be enforced because it violated public policy and thus should not be given effect by any court of justice. Justice Field dissented from this decision, arguing that while contracts which violate public policy are generally unenforceable, there is no reason why such a contract cannot still have some legal effect if both parties were aware of its illegality at the time they entered into it and agreed to abide by its terms anyway. He argued further that since all laws are based on principles of morality and justice, allowing courts to enforce contracts which violate them would actually serve to strengthen those same principles rather than weaken them as suggested by the majority opinion.