Bethell v. Demaret was a United States Supreme Court case that dealt with the issue of whether a state court could issue a writ of habeas corpus to a prisoner held in a federal prison. The case arose when a prisoner, Bethell, was held in a federal prison in the state of Missouri. Bethell sought a writ of habeas corpus from the state court, which was denied by the federal 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 prerogative and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also held that the writ of habeas corpus was a fundamental right that could not be denied by the state court. The Court's decision in Bethell v. Demaret established that the writ of habeas corpus was a federal prerogative and that state courts could not interfere with the federal government's power to imprison individuals.

In Bethell v. Demaret, the Supreme Court of the United States was asked to decide whether a state court had jurisdiction over an action brought by a non-resident against another non-resident in which both parties were citizens of different states. The majority opinion held that such suits could not be maintained in state courts because they would interfere with Congress’s power to regulate interstate commerce and foreign relations under Article I, Section 8 of the Constitution. However, Justice Field dissented from this ruling on two grounds: firstly, he argued that there was no evidence that Congress intended for its powers under Article I to extend so far as to deprive states of their right to adjudicate disputes between citizens; secondly, he argued that even if it did have such authority it should only be exercised when necessary and proper for carrying into execution some other enumerated power granted by the Constitution. He concluded his dissent by stating “the question is one purely judicial…and should not be decided upon any general considerations or abstract principles” but rather based on what is actually written in the Constitution itself.