United States v. Arwo was a United States Supreme Court case that dealt with the issue of whether a foreign corporation could be sued in a United States court. The case involved a dispute between the United States and a German corporation, Arwo, over a contract for the sale of goods. The United States argued that Arwo was subject to the jurisdiction of the United States court, while Arwo argued that it was not. The Supreme Court held that a foreign corporation could be sued in a United States court if it had sufficient contacts with the United States. The Court found that Arwo had sufficient contacts with the United States, as it had entered into a contract with a United States citizen, and had shipped goods to the United States. Therefore, the Court held that Arwo was subject to the jurisdiction of the United States court. The Court's decision in United States v. Arwo established the principle that foreign corporations can be sued in United States courts if they have sufficient contacts with the United States. This principle has been applied in numerous cases since then, and has become an important part of United States law.

In United States v. Arwo, the Supreme Court was asked to decide whether a defendant could be convicted of violating an act of Congress when the alleged offense occurred before that act had been passed. The majority opinion held that such convictions were permissible under certain circumstances, but Justice Field dissented from this ruling. He argued that it would be unconstitutional for Congress to pass laws with retroactive effect and thereby punish individuals for acts which were not considered criminal at the time they occurred. Furthermore, he noted that if such legislation was allowed then there would be no limit on how far back in time a law could reach or what type of conduct it might cover; thus allowing arbitrary punishments without due process protections being afforded to those accused of crimes.