French v. Hopkins was a United States Supreme Court case that addressed the issue of whether a state court had the authority to issue a writ of mandamus to a federal court. The case involved a dispute between two parties, French and Hopkins, over a contract for the sale of a steamboat. French had obtained a judgment in a state court in Louisiana, and Hopkins had appealed the decision to the federal court. The state court then issued a writ of mandamus to the federal court, ordering it to hear the case. The Supreme Court held that the state court did not have the authority to issue the writ of mandamus to the federal court. The Court reasoned that the state court lacked jurisdiction over the federal court, and that the writ of mandamus was an inappropriate remedy for the dispute. The Court also noted that the writ of mandamus was not necessary to ensure that the federal court heard the case, as the federal court was already obligated to do so. The Court's decision in French v. Hopkins established that state courts do not have the authority to issue writs of mandamus to federal courts. This decision has been cited in numerous subsequent cases, and remains an important precedent in the area of federal-state court relations.

Justice Field delivered the dissenting opinion in French v. Hopkins, arguing that the majority’s decision was contrary to both law and equity. He argued that under California law, a contract for personal services could not be assigned without consent of all parties involved. The plaintiff had entered into an agreement with another party who then assigned his rights to the defendant without obtaining permission from either party involved in the original contract; thus, Justice Field believed this assignment should have been declared void by the court as it violated California state laws governing contracts for personal services. Furthermore, he argued that even if such assignments were allowed under California law, they would still be subject to equitable principles which require consideration or some form of compensation when assigning contractual obligations between two parties; however no such consideration had been provided here and therefore any assignment made was invalid according to these principles as well. In conclusion Justice Field asserted that since there was no valid transfer of rights between these two parties due to lack of consent or consideration given by either side, then there can be no liability on behalf of either one towards fulfilling their respective contractual obligations and thus judgment should have been rendered in favor of plaintiff instead