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.

Justice Field delivered the dissenting opinion in Erhardt v. Boaro & Others, arguing that the majority had misinterpreted a provision of California law and failed to consider its implications for contract formation. He argued that under California's Civil Code, contracts could be formed without consideration if they were made in writing and signed by both parties; however, he noted that this was not applicable to certain types of agreements such as those involving real estate or marriage settlements. Furthermore, Justice Field argued that even though there was no consideration present when the agreement between Erhardt and Boaro was made, it should still be enforced because it met all other requirements for a valid contract under California law - namely being written down and signed by both parties. In conclusion, Justice Field believed that since there was sufficient evidence indicating an intention on behalf of both parties to enter into an enforceable agreement at the time it was created then this should have been taken into account when deciding whether or not to uphold their contractual obligations towards each other.