Mellen v. Wallach was a United States Supreme Court case that addressed the issue of whether a state court could enjoin a federal court from hearing a case. The case involved a dispute between two parties over a contract for the sale of a steamboat. The plaintiff, Mellen, had filed a suit in a federal court in Louisiana to recover damages for the breach of the contract. The defendant, Wallach, then filed a suit in a state court in Louisiana seeking an injunction to prevent the federal court from hearing the case. The Supreme Court held that the state court did not have the authority to enjoin the federal court from hearing the case. The Court reasoned that the state court was not authorized to interfere with the proceedings of the federal court, as the federal court had exclusive jurisdiction over the case. The Court further noted that the state court was not authorized to interfere with the proceedings of the federal court, as the federal court had exclusive jurisdiction over the case. The Court also held that the state court was not authorized to issue an injunction against the federal court, as the state court lacked the power to control the proceedings of the federal court. The Court noted that the state court could not interfere with the proceedings of the federal court, as the federal court had exclusive jurisdiction over the case. In conclusion, the Supreme Court held that the state court did not have the authority to enjoin the federal court from hearing the case. The Court reasoned that the state court was not authorized to interfere with the proceedings of the federal court, as the federal court had exclusive jurisdiction over the case.

Justice Field delivered the dissenting opinion in Mellen v. Wallach, arguing that the majority's decision was incorrect and should be reversed. He argued that a contract between two parties is binding on both of them, regardless of whether one party had knowledge or not about certain facts related to it. In this case, he believed that even though Wallach did not know all the details regarding his agreement with Mellen when he signed it, he still had an obligation to fulfill its terms as written. Furthermore, Justice Field argued that if a court were to allow one party to escape their contractual obligations due solely because they lacked knowledge at the time of signing then contracts would become meaningless and unenforceable by law. As such, Justice Field concluded that since there was no evidence presented showing any fraud or misrepresentation on either side during negotiations for this particular contract then Wallach must abide by its terms as agreed upon and pay Mellen what was owed him according to those conditions.