Hartranft v. Du Pont was a United States Supreme Court case that addressed the issue of whether a patentee could sue for infringement of a patent in a state court. The case involved a patent for a process of manufacturing gunpowder, which was owned by the plaintiff, Hartranft. The defendant, Du Pont, had been using the process without Hartranft's permission. The Supreme Court held that Hartranft had the right to sue Du Pont for patent infringement in a state court. The Court reasoned that the patent laws of the United States gave the patentee the exclusive right to use the invention, and that this right was enforceable in state courts. The Court also noted that the patent laws of the United States did not limit the right of a patentee to sue for infringement in a state court. The Court's decision in Hartranft v. Du Pont established that patentees have the right to sue for infringement in state courts. This decision has been cited in numerous subsequent cases, and has been used to support the right of patentees to sue for infringement in state courts.

Justice Field delivered the dissenting opinion in Hartranft v. Du Pont, arguing that the majority had failed to consider a key point of law. He argued that under Pennsylvania state law, when an individual is injured by another's negligence and subsequently dies from those injuries, their personal representative can bring a wrongful death action on behalf of the deceased person's estate. In this case, he argued that since Hartranft was killed due to Du Pont’s negligence and his widow was appointed as his personal representative shortly after his death, she should have been allowed to pursue her claim for damages against Du Pont on behalf of her husband’s estate. Justice Field further noted that even if there were any doubts about whether or not Mrs. Hartranft could sue on behalf of her late husband’s estate under Pennsylvania state law (which he did not believe existed), it would be up to the Supreme Court of Pennsylvania—not the U.S Supreme Court—to make such a determination based upon its interpretation of applicable state laws and precedents set forth by prior cases decided within its jurisdiction