United States v. Ballard et al. was a case heard by the United States Supreme Court in 1871. The case involved the prosecution of two individuals, George Ballard and Charles B. Reynolds, for fraudulently obtaining a patent from the United States Patent Office. Ballard and Reynolds had submitted a patent application for a machine that they claimed could produce a new type of fuel. The patent office granted the patent, but the machine was later found to be a fraud. The Supreme Court ruled that the patent office had acted in good faith in granting the patent, and that the patent was valid. However, the Court also held that Ballard and Reynolds had committed fraud in obtaining the patent, and that they were liable for damages. The Court also held that the patent office had a duty to investigate patent applications before granting them, and that it should have done so in this case. The Court's ruling established the principle that the patent office must exercise due diligence in examining patent applications.

In United States v. Ballard et al., the Supreme Court was tasked with determining whether or not a spiritualist movement, which claimed to be able to communicate with spirits of the dead, constituted fraud and violated federal law. The majority opinion held that it did constitute fraud and thus violated federal law; however, Justice Field dissented from this ruling. He argued that while some members of the spiritualist movement may have been fraudulent in their practices, there was no evidence presented by either side as to how many were actually engaging in such activities nor any proof that those who believed they could contact spirits had done so for financial gain or other criminal purposes. Therefore he concluded that Congress should not interfere with religious beliefs unless there is clear evidence of wrongdoing on behalf of its adherents.