Kramer v. Cohn 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 person who was being held in custody by a private individual. The case arose when a man named Kramer was arrested by a private individual, Cohn, and held in custody without a warrant. Kramer then sought a writ of habeas corpus from a state court, which was granted. Cohn then 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 person who was being held in custody by a private individual. The Court reasoned that the writ of habeas corpus was a remedy that was available only to persons who were being held in custody by a public official, such as a sheriff or a jailer. The Court also noted that the writ of habeas corpus was not available to persons who were being held in custody by a private individual, such as Cohn. Therefore, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to Kramer, and the decision of the state court was reversed. This case established the principle that a writ of habeas corpus is not available to persons who are being held in custody by a private individual.

In Kramer v. Cohn, the United States Supreme Court was asked to decide whether a state court had jurisdiction over a case involving an alleged breach of contract between two parties from different states. The majority opinion held that the state court did not have jurisdiction because it lacked diversity of citizenship among the parties involved in the dispute. Justice Field dissented, arguing that under Article III of the Constitution, Congress has authority to confer on state courts original jurisdiction over cases arising out of contracts made between citizens from different states and territories. He argued further that such power should be exercised by Congress when necessary for justice and convenience as long as it does not conflict with any other provision in either federal or state law. In this particular case, he believed there was no reason why Congress could not grant original jurisdiction to the New York State court since both parties were citizens within its boundaries at all times relevant to their dispute and thus subject to its laws governing contracts entered into within its borders.