United States v. Ames is a United States Supreme Court case that dealt with the issue of whether a defendant could be convicted of a crime if the statute of limitations had expired. The case involved a defendant, William Ames, who was charged with a crime that had a three-year statute of limitations. The government argued that the statute of limitations had been tolled due to the defendant's absence from the jurisdiction. The Supreme Court held that the statute of limitations had not been tolled and that the defendant could not be convicted of the crime. The Court reasoned that the statute of limitations was a substantive right that could not be taken away by the government. The Court further reasoned that the defendant's absence from the jurisdiction did not constitute a waiver of the statute of limitations. The Court held that the statute of limitations was an absolute bar to prosecution and that the defendant could not be convicted of the crime. The Court's decision in United States v. Ames established that the statute of limitations is an absolute bar to prosecution and that the government cannot toll the statute of limitations by arguing that the defendant was absent from the jurisdiction. The decision also established that the statute of limitations is a substantive right that cannot be taken away by the government.

In United States v. Ames, the Supreme Court was asked to decide whether a tax imposed on distilled spirits by Congress in 1868 was constitutional. The majority opinion held that it was, finding that Congress had the power to impose taxes for revenue purposes under its broad authority granted by Article I of the Constitution. Justice Field dissented from this decision, arguing that while Congress did have some limited powers over taxation and spending, they were not unlimited and could not be used as an excuse for any type of taxation or regulation desired by Congress. He argued further that if such expansive powers were allowed then there would be no limit on what kind of taxes or regulations could be imposed upon citizens without their consent - something which he felt violated both the spirit and letter of the Constitution's protections against government interference with individual rights.