Flanders v. Tweed 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 a prisoner, Flanders, was held in a federal prison in California and sought a writ of habeas corpus from the California Supreme Court. The California Supreme Court granted the writ, but the federal government argued that the state court did not have the authority to issue the writ. The Supreme Court ultimately 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 power, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's power to protect this right. The decision in Flanders v. Tweed was significant because it established that the state courts did 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 it has been used to support the idea that the federal government has the power to protect the fundamental right of habeas corpus.

In Flanders v. Tweed, the Supreme Court was asked to decide whether a contract between two parties could be enforced if it violated state law. The majority opinion held that such contracts were not enforceable and thus dismissed the case. However, Justice Field dissented from this decision on the grounds that enforcing such contracts would promote justice and fairness in commercial transactions. He argued that when two parties enter into an agreement with full knowledge of its illegality under state law, they should still be allowed to rely upon it as long as no public policy is violated by doing so. Furthermore, he asserted that allowing courts to refuse enforcement of these agreements would lead to uncertainty in business dealings and ultimately harm commerce more than upholding them ever could.