Forsyth v. Doolittle was a United States Supreme Court case that addressed the issue of whether a state court had the authority to issue an injunction against a federal officer. The case arose when the plaintiff, Forsyth, sought an injunction against the defendant, Doolittle, who was a federal officer. Forsyth alleged that Doolittle had violated the terms of a contract between the two parties. The state court granted the injunction, and Doolittle appealed to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue an injunction against a federal officer. The Court reasoned that the federal government had exclusive authority over its officers, and that the state court did not have the power to interfere with the federal government's authority. The Court also noted that the state court's injunction would have interfered with the federal government's ability to carry out its duties. The Court's decision in Forsyth v. Doolittle established that state courts do not have the authority to issue injunctions against federal officers. This decision has been cited in numerous subsequent cases, and it remains an important precedent in the area of federal-state relations.

In Forsyth v. Doolittle, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving an alleged breach of contract between two citizens of different states. The majority opinion held that the state court did not have jurisdiction because it lacked diversity among the parties involved in the dispute and thus could not exercise its authority under federal law. Justice Field dissented from this decision, arguing that Congress had given state courts concurrent jurisdiction with federal courts in such cases and therefore they should be allowed to hear them regardless of any lack of diversity among those involved. He further argued that allowing only federal courts to hear these types of disputes would create unnecessary delays for litigants who may need speedy resolution due to their financial circumstances or other reasons related to their particular situation.