Penn v. Calhoun 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 held in a federal prison. The case arose when the state of Pennsylvania attempted to issue a writ of habeas corpus to a prisoner held in a federal prison in the state of Maryland. The prisoner, William Calhoun, had been convicted of a federal crime and was serving his sentence in the 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 it. The Court further held that the state court could not interfere with the federal government's power to enforce its laws. The Court's decision in Penn v. Calhoun established the principle 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 power to enforce its laws.

Justice Field delivered the dissenting opinion in Penn v. Calhoun, arguing that the majority had misconstrued the law and failed to consider certain facts of the case. He argued that under California law, a married woman could not be held liable for her husband's debts unless she was specifically named as a party to them or had given her consent by signing documents related to them. In this case, neither of these conditions were met; therefore, Justice Field believed Mrs. Penn should not have been held liable for Mr. Calhoun's debt since it was incurred before their marriage and without her knowledge or consent. Furthermore, he noted that even if Mrs. Penn did owe money on behalf of her husband due to his negligence in failing to pay his creditors after their marriage - which he doubted - such an obligation would only extend until she obtained a legal separation from him through divorce proceedings; however no such action had taken place at this time so any claim against Mrs. Penn should have been dismissed by the court below according to California law at that time period