Hannauer v. Woodruff was a United States Supreme Court case that dealt with the issue of whether a contract between two parties was valid. The case involved a contract between two parties, Hannauer and Woodruff, in which Hannauer agreed to pay Woodruff a certain sum of money in exchange for a certain piece of property. Woodruff had already sold the property to another party, and Hannauer argued that the contract was invalid because Woodruff had no right to sell the property. The Supreme Court ruled in favor of Hannauer, finding that the contract was valid and that Woodruff had no right to sell the property. The Court held that a contract is valid if it is made in good faith and with the intention of fulfilling the terms of the agreement. The Court also held that a contract is not invalidated by the fact that one of the parties has already sold the property in question. The Court found that the contract was valid and that Hannauer was entitled to the money he had agreed to pay Woodruff.

In Hannauer v. Woodruff, the Supreme Court was tasked with determining whether a state court had jurisdiction over a case involving two citizens of different states. The majority opinion held that the state court did have jurisdiction in this matter and affirmed its decision. However, Justice Field dissented from this opinion on the grounds that it violated Article III of the Constitution which grants federal courts exclusive jurisdiction over cases between citizens of different states. He argued that allowing state courts to hear such cases would create an unnecessary burden for litigants who must travel long distances to appear before them and could lead to conflicting decisions if both parties were allowed to bring their claims in separate forums. Furthermore, he noted that Congress has not granted any authority for such proceedings and thus they should be left exclusively within federal control as mandated by Article III of the Constitution