Moore v. Marsh was a United States Supreme Court case that was decided in 1868. The case involved a dispute between two parties over the ownership of a piece of land in the state of Missouri. The plaintiff, Moore, claimed that he had purchased the land from the defendant, Marsh, and that Marsh had failed to deliver the deed to the property. Marsh argued that he had never sold the land to Moore and that Moore had no legal claim to the property. The Supreme Court ultimately sided with Moore, ruling that he had a valid claim to the land. The Court held that Moore had provided sufficient evidence to prove that he had purchased the land from Marsh, and that Marsh had failed to deliver the deed. The Court also held that Moore had a right to the land under the doctrine of equitable estoppel, which states that a person cannot deny a contract that they have previously agreed to. The decision in Moore v. Marsh established the principle that a person cannot deny a contract that they have previously agreed to, and that a person who has purchased land has a valid claim to the property even if the deed has not been delivered. This decision has been cited in numerous cases since its ruling in 1868.

In Moore v. Marsh, the Supreme Court was asked to decide whether a state court had jurisdiction over an action brought by a citizen of one state against another in which the amount in controversy exceeded $500. The majority opinion held that it did not have such jurisdiction and dismissed the case. In dissent, Justice Field argued that this decision would lead to "great injustice" as citizens of different states could be denied access to justice due to jurisdictional issues. He further argued that since Congress has granted federal courts exclusive original jurisdiction over cases between citizens of different states where the amount exceeds $500, then logically they should also grant concurrent jurisdiction with state courts for such cases so long as both parties consent or waive their right to remove it from state court into federal court. This would ensure equal protection under law and provide greater access for all litigants regardless of their citizenship status or financial means.