Elgin v. Marshall was a United States Supreme Court case that addressed the issue of whether a state court could issue a writ of mandamus to a federal court. The case involved a dispute between the City of Elgin, Illinois and the Marshall family over the ownership of a piece of property. The Marshall family had obtained a judgment from the state court granting them title to the property, but the City of Elgin refused to comply with the judgment. The Marshall family then sought a writ of mandamus from the state court, ordering the City of Elgin to comply with the judgment. The Supreme Court held that the state court did not have the authority to issue a writ of mandamus to a federal court. The Court reasoned that the writ of mandamus was a form of judicial power, and that the state court did not have the authority to exercise judicial power over a federal court. The Court also noted that the writ of mandamus was a form of extraordinary relief, and that the state court did not have the authority to grant such relief to a federal court. The Court's decision in Elgin v. Marshall 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 has been used to support the principle that state courts cannot exercise judicial power over federal courts.

In Elgin v. Marshall, the Supreme Court was tasked with determining whether a state court had jurisdiction to issue an injunction against a railroad company for operating its trains in violation of local ordinances. The majority opinion held that the state court did not have such authority and reversed the decision of the lower courts. Justice Field dissented from this ruling, arguing that states should be allowed to exercise their police powers over railroads within their borders as long as they do not conflict with federal laws or regulations. He argued that Congress has given states broad discretion when it comes to regulating public safety and health matters related to railroads, so long as those regulations are reasonable and consistent with federal law. Furthermore, he noted that while Congress may preempt certain areas of regulation by passing legislation on them directly, it has yet to do so in regards to railroad operations; thus allowing states some leeway in how they choose regulate these activities within their own borders is appropriate under existing law.